Self-controlled Risk Interval Design Research Articles

Applying two approaches to detect unmeasured confounding due to time-varying variables in a self-controlled risk interval design evaluating COVID-19 vaccine safety signals, using myocarditis as a case example.

We test the robustness of the self-controlled risk interval (SCRI) design in a setting where time between doses may introduce time-varying confounding, using both negative control outcomes (NCOs) and quantitative bias analysis (QBA). All vaccinated cases identified from 5 European databases between 1 September 2020 and end of data availability were included. Exposures were doses 1-3 of the Pfizer, Moderna, AstraZeneca, and Janssen COVID-19 vaccines; outcomes were myocarditis and otitis externa (NCO). The SCRI used a 60-day control window and dose-specific 28-day risk windows, stratified by vaccine brand and adjusted for calendar time. The QBA included two scenarios: (i) baseline probability of the confounder was higher in the control window and (ii) vice versa. The NCO was not associated with any of the COVID-19 vaccine types or doses except Moderna dose 1 (IRR = 1.09, 95%CI 1.01-1.09). The QBA suggested even the strongest literature-reported confounder (COVID-19; RRmyocarditis = 18.3) could only explain away part of the observed effect from IRR = 3 to IRR = 1.40. The SCRI seems robust to unmeasured confounding in the COVID-19 setting, although a strong unmeasured confounder could bias the observed effect upward. Replication of our findings for other safety signals would strengthen this conclusion.

Importance of Examining Incidentality in Vaccine Safety Assessment

The author believes that the principles of statistical methods for vaccine safety can be divided into three categories: comparison of adverse event incidence rates between vaccinated and unvaccinated groups, analysis of incidentality in the vaccinated group, and a combination of both. The first category includes the cohort study; the second, the self-controlled risk interval design (SCRI); and the third, the self-controlled case series method. A single p-value alone should not determine a scientific conclusion, and analysis should be performed using multiple statistical methods with different principles. The author believes that using both the cohort study and the SCRI for analysis is the best method to assess vaccine safety. When the cohort study may not detect a significant difference owing to a low incidence rate of an adverse event in the vaccinated group or a high one in the unvaccinated group, the SCRI may detect it. Because vaccines must have a higher level of safety than the pharmaceuticals used for treatment, vaccine safety is advisable to be assessed using methods that can detect a significant difference even for any value of the incidence rate of an adverse event. The author believes that the analyses of COVID-19 vaccine safety have areas for improvement because the proportion of papers that used the cohort study and the SCRI was negligible.

The Effect of COVID-19 Vaccination on Outpatient Antibiotic Prescribing in Older Adults: A Self-Controlled Risk-Interval Study.

Coronavirus disease 2019 (COVID-19) vaccination has been associated with reduced outpatient antibiotic prescribing among older adults with laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We assessed the impact of COVID-19 vaccination on outpatient antibiotic prescribing in the broader population of older adults, regardless of SARS-CoV-2 infection status. We included adults aged ≥65 years who received their first, second, and/or third COVID-19 vaccine dose from December 2020 to December 2022. We used a self-controlled risk-interval design and included cases who received an antibiotic prescription 2-6 weeks before vaccination (pre-vaccination or control interval) or after vaccination (post-vaccination or risk interval). We used conditional logistic regression to estimate the odds of being prescribed (1) any antibiotic, (2) a typical "respiratory" infection antibiotic, or (3) a typical "urinary tract" infection antibiotic (negative control) in the post-vaccination interval versus the pre-vaccination interval. We accounted for temporal changes in antibiotic prescribing using background monthly antibiotic prescribing counts. 469 923 vaccine doses met inclusion criteria. The odds of receiving any antibiotic or a respiratory antibiotic prescription were lower in the post-vaccination versus pre-vaccination interval (aOR, .973; 95% CI, .968-.978; aOR, .961; 95% CI, .953-.968, respectively). There was no association between vaccination and urinary antibiotic prescriptions (aOR, .996; 95% CI, .987-1.006). Periods with high (>10%) versus low (<5%) SARS-CoV-2 test positivity demonstrated greater reductions in antibiotic prescribing (aOR, .875; 95% CI, .845-.905; aOR, .996; 95% CI, .989-1.003, respectively). COVID-19 vaccination was associated with reduced outpatient antibiotic prescribing in older adults, especially during periods of high SARS-CoV-2 circulation.

Effectiveness of COVID-19 vaccines against severe outcomes in cancer patients: Real-world evidence from self-controlled risk interval and retrospective cohort studies

BackgroundThe effectiveness of COVID-19 vaccines is generally reduced in cancer patients compared to the general population. However, there are only a few studies that compare the relative risk of breakthrough infections and severe COVID-19 outcomes in fully vaccinated cancer patients versus their unvaccinated counterparts. MethodsTo assess the effectiveness of COVID-19 vaccines in cancer patients, we employed (1) a self-controlled risk interval (SCRI) design, and (2) a retrospective matched cohort design. A SCRI design was used to compare the risk of breakthrough infection in vaccinated cancer patients during the period immediately following vaccination (“control window”) and the period in which immunity is achieved (“exposure windows”). The retrospective matched cohort design was used to compare the risk of severe COVID-19 outcomes between vaccinated and unvaccinated cancer patients. For both studies, data were extracted from the Korea Disease Control and Prevention Agency-COVID-19-National Health Insurance Service cohort, including demographics, medical history, and vaccination records of all individuals confirmed with COVID-19. We used conditional Poisson regression to calculate the incidence rate ratio (IRR) for breakthrough infection and Cox regression to estimate the hazard ratio (HR) for severe outcomes. ResultsOf 14,448 cancer patients diagnosed with COVID-19 between October 2020 and December 2021, a total of 217 and 3996 cancer patients were included in the SCRI and cohort study respectively. While the risk of breakthrough infections, measured by the incidence rate in the control and exposure windows, did not show statistically significant difference in vaccinated cancer patients (IRR=0.88, 95% CI: 0.64–1.22), the risk of severe COVID-19 outcomes was significantly lower in vaccinated cancer patients compared to those unvaccinated (HR=0.27, 95% CI: 0.22–0.34). ConclusionCOVID-19 vaccines significantly reduce the risk of severe outcomes in cancer patients, though their efficacy against breakthrough infections is less evident.

Cardiovascular, Neurological, and Immunological Adverse Events and the 23-Valent Pneumococcal Polysaccharide Vaccine

Despite widespread immunization with the 23-valent pneumococcal polysaccharide vaccine (PPSV23), safety concerns remain owing to a lack of statistical power and largely outdated evidence. To evaluate the association between cardiovascular, neurological, and immunological adverse events and PPSV23 vaccination in older adults. This population-based cohort study using a self-controlled risk interval design used a large linked database created by linking the Korea Immunization Registry Information System and the National Health Information Database (2018 to 2021). Participants included patients aged 65 years or older with a history of PPSV23 vaccination and incident cardiovascular, neurological, or immunological events during the risk and control intervals. Data were analyzed from November 2022 to April 2023. 23-valent pneumococcal polysaccharide vaccine. The occurrence of 1 among 6 cardiovascular events (myocardial infarction, atrial fibrillation, cardiomyopathy, heart failure, hypotension, and myocarditis or pericarditis), 2 neurological events (Bell palsy and Guillain-Barré syndrome), and 3 immunological events (sepsis, thrombocytopenia, and anaphylaxis) during the risk and control periods. The risk and control intervals were defined as 1 to 28 and 57 to 112 days after PPSV23 vaccination, respectively. Conditional Poisson regression was used to estimate the incidence rate ratio (IRR) with a 95% CI. Altogether, 4355 of the 1 802 739 individuals who received PPSV23 vaccination and experienced at least 1 outcome event were included (mean [SD] age, 72.4 [8.2] years; 2272 male participants [52.1%]). For cardiovascular events, there were no significant associations for myocardial infarction (IRR, 0.96; 95% CI, 0.81-1.15), heart failure (IRR, 0.85; 95% CI, 0.70-1.04), and stroke (IRR, 0.92; 95% CI, 0.84-1.02). Similarly, no increased risks were observed for neurological and immunological outcomes: Bell palsy (IRR, 0.95; 95% CI, 0.72-1.26), Guillain-Barré syndrome (IRR, 0.27; 95% CI, 0.06-1.17), sepsis (IRR, 0.99; 95% CI, 0.74-1.32), and thrombocytopenia (IRR, 1.18; 95% CI, 0.60-2.35). In this self-controlled risk interval study, there was no appreciable increase in risk for most cardiovascular, neurological, or immunological adverse events following PPSV23. The updated safety profile of PPSV23 provides supportive evidence for the establishment of immunization strategies for older adults.

Incidence of venous thromboembolism with immune checkpoint inhibitors in a community setting: A single-center retrospective study.

e14681 Background: Immune activation and inflammation caused by immune checkpoint inhibitors (ICIs) are critical pathobiological drivers for venous thromboembolism (VTE). There is a paucity of data about VTE risk in cancer patients receiving ICI. We aimed to describe the incidence of VTE in cancer patients receiving ICI in a community setting. Methods: We conducted a single center, retrospective cohort study at Saint Vincent Hospital. The study cohort was created using our center's pharmacy database of patients who received any of the five ICIs (ipilimumab, nivolumab, pembrolizumab, atezolizumab, or durvalumab) between Jan 2017 and Dec 2022. VTE events including deep venous thrombosis, splanchnic vein thrombosis, and pulmonary embolism, were identified by chart review. We used a self-controlled risk-interval design, with "control period" and "at-risk period" being 6 months before and after the initiation of ICI treatment respectively. VTE events were also analyzed for subgroups: Single-agent ICI therapy (IA), Dual ICI therapy (IB), and ICI + chemotherapy (IC). Descriptive statistics and cox regression were used for statistical analysis. Results: Study population included 170 patients, with 75, 14, and 81 patients in subgroups IA, IB, and IC respectively. The mean age of the patients was 69.51 ± 10.05 years with a majority being males (62.4%). The most common cancer observed was non-small cell lung cancer (43.5%) followed by small cell lung cancer (6.9%), and malignant melanoma (5.7%). Pembrolizumab (55.3%) was the most common ICI used and nivolumab + ipilimumab (7.64%) was the most common dual ICI used. We noted a 1.25-fold higher incidence of VTE post-ICI use (Incidence rate ratio [IRR]: 11.76 per 100 person-year) compared to pre-ICI use (IRR: 9.41 per 100 person-year) at 6 months. On subgroup analysis, Group IB had the highest risk for VTE at 6 months (IRR: 28.57 per 100 person-year), followed by group IC and IA (IRR: 14.12 and 8.0 per 100 person-year respectively). IRR decreased to 6.62 per 100 person-year at 12-month interval indicating increased VTE risk in the first 6 months of ICI exposure. Type of ICI, adjuvant chemotherapy or type of cancer was not able to predict VTE risk on multivariate analysis. Conclusions: ICI treatment was associated with an increased incidence of VTE in our study cohort with the highest risk among patients on dual ICI followed by ICI + chemotherapy and ICI monotherapy. Future prospective studies are needed to identify risk factors and biomarkers to improve risk stratification and risk-adapted thromboprophylaxis.[Table: see text]

Safety of measles, mumps, and rubella vaccine in adolescents and adults in the vaccine safety Datalink

Measles, mumps, and rubella vaccine (MMR) is routinely administered to children; however, adolescents and adults may receive MMR for various reasons. Safety studies in adolescents and adults are limited. We report on safety of MMR in this age group in the Vaccine Safety Datalink. We included adolescents (aged 9-17years) and adults (aged≥18years) who received≥1 dose of MMR from January 1, 2010-December 31, 2018. Pre-specified outcomes were identified by diagnosis codes. Clinically serious outcomes included anaphylaxis, encephalitis/myelitis, Guillain-Barré syndrome, immune thrombocytopenia, meningitis, and seizure. Non-serious outcomes were allergic reaction, arthropathy, fever, injection site reaction, lymphadenopathy, non-specific reaction, parotitis, rash, and syncope. All serious outcomes underwent medical record review. Outcome-specific incidence was calculated in pre-defined post-vaccination windows. A self-controlled risk interval design was used to determine the relative risk of each outcome in a risk window after vaccination compared to a more distal control window. During the study period, 276,327 MMR doses were administered to adolescents and adults. Mean age of vaccinees was 34.8years; 65.8% were female; 53.2% of doses were administered simultaneously with≥1 other vaccine. Serious outcomes were rare, with incidence≤6 per 100,000 doses for each outcome assessed, and none had a significant elevation in incidence during the risk window compared to the control window. Incidence of non-serious outcomes per 100,000 doses ranged from 3.4 for parotitis to 263.0 for arthropathy. Other common outcomes included injection site reaction and rash (157.0 and 112.9 per 100,000 doses, respectively). Significantly more outcomes were observed during the risk window compared to the control window for all non-serious outcomes except parotitis. Some variability was observed by sex and age group. Serious outcomes after MMR are rare in adolescents and adults, but vaccinees should be counseled regarding anticipated local and systemic non-serious adverse events.

Assessment of Herpes Zoster Risk Among Recipients of COVID-19 Vaccine

Herpes zoster infection after COVID-19 vaccination has been reported in numerous case studies. It is not known whether these cases represent increased reporting or a true increase in risk. To assess whether COVID-19 vaccination is associated with an increased risk of herpes zoster infection. This cohort study used a self-controlled risk interval (SCRI) design to compare the risk of herpes zoster in a risk interval of 30 days after COVID-19 vaccination or up to the date of the second vaccine dose with a control interval remote from COVID-19 vaccination (defined as 60-90 days after the last recorded vaccination date for each individual, allowing for a 30-day washout period between control and risk intervals). A supplemental cohort analysis was used to compare the risk of herpes zoster after COVID-19 vaccination with the risk of herpes zoster after influenza vaccination among 2 historical cohorts who received an influenza vaccine in the prepandemic period (January 1, 2018, to December 31, 2019) or the early pandemic period (March 1, 2020, to November 30, 2020). Data were obtained from Optum Labs Data Warehouse, a US national deidentified claims-based database. A total of 2 039 854 individuals who received any dose of a COVID-19 vaccine with emergency use authorization (BNT162b2 [Pfizer-BioNTech], mRNA-1273 [Moderna], or Ad26.COV2.S [Johnson & Johnson]) from December 11, 2020, through June 30, 2021, were eligible for inclusion. Individuals included in the SCRI analysis were a subset of the COVID-19-vaccinated cohort who had herpes zoster during either a risk or control interval. Any dose of a COVID-19 vaccine. Incident herpes zoster, defined by International Statistical Classification of Diseases and Related Health Problems, Tenth Revision codes and a prescription of a new antiviral medication or a dose increase in antiviral medication within 5 days of diagnosis. Among 2 039 854 individuals who received any dose of a COVID-19 vaccine during the study period, the mean (SD) age was 43.2 (16.3) years; 1 031 149 individuals (50.6%) were female, and 1 344 318 (65.9%) were White. Of those, 1451 patients (mean [SD] age, 51.6 [12.6] years; 845 [58.2%] female) with a herpes zoster diagnosis were included in the primary SCRI analysis. In the SCRI analysis, COVID-19 vaccination was not associated with an increased risk of herpes zoster after adjustment (incidence rate ratio, 0.91; 95% CI, 0.82-1.01; P = .08). In the supplementary cohort analysis, COVID-19 vaccination was not associated with a higher risk of herpes zoster compared with influenza vaccination in the prepandemic period (first dose of COVID-19 vaccine: hazard ratio [HR], 0.78 [95% CI, 0.70-0.86; P < .001]; second dose of COVID-19 vaccine: HR, 0.79 [95% CI, 0.71-0.88; P < .001]) or the early pandemic period (first dose of COVID-19 vaccine: HR, 0.89 [95% CI, 0.80-1.00; P = .05]; second dose: HR, 0.91 [95% CI, 0.81-1.02; P = .09]). In this study, there was no association found between COVID-19 vaccination and an increased risk of herpes zoster infection, which may help to address concerns about the safety profile of the COVID-19 vaccines among patients and clinicians.

Self-controlled assessment of thromboembolic event (TEE) risk following intravenous immune globulin (IGIV) in the U.S. (2006-2012).

Since 2013, the U.S. Food and Drug administration (FDA) has required that intravenous immune globulin (IGIV) products carry a boxed warning concerning the risk of thromboembolic events (TEEs). This study assessed the incidence of TEEs attributable to IGIV in a large population-based cohort. A self-controlled risk interval design was used to quantify the transient increase in TEE risk during the risk interval (days 0-2 and 0-13 following IGIV for arterial and venous TEEs, respectively) relative to a later control interval (days 14-27 following IGIV). Potential IGIV-exposed TEE cases from 2006 to 2012 were identified from the FDA-sponsored Sentinel Distributed Database and confirmed through medical record review. Inpatient IGIV exposures were not included in the venous TEE analysis due to concerns about time-varying confounding. 19,069 new users of IGIV who received 93,555 treatment episodes were included. Charts were retrieved for 62% and 70% of potential venous and arterial cases, respectively. There was a transient increase in the risk of arterial TEEs during days 0-2 following IGIV treatment (RR = 4.69; 95% CI 1.87, 11.90; absolute increase in risk = 8.86 events per 10,000 patients, 95% CI 3.25, 14.6), but no significant increase in venous TEE risk during days 0-13 following outpatient IGIV treatments (RR = 1.07, 95% CI 0.34, 3.48). Our results suggest there is a small increase in the absolute risk of arterial TEEs following IGIV. However, lower-than-expected chart retrieval rates and the possibility of time-varying confounding mean that our results should be interpreted cautiously. Continued pharmacovigilance efforts are warranted.

Immune checkpoint inhibitors for cancer and venous thromboembolic events

BackgroundImmune checkpoint inhibitors (ICIs) are widely used cancer treatments. There are limited data on the risk for developing venous thromboembolism (VTE) among patients on an ICI. MethodsThis was a retrospective study of 2854 patients who received ICIs at a single academic centre. VTE events, defined as a composite of deep vein thrombosis or pulmonary embolism, were identified by individual chart review and blindly adjudicated using standard imaging criteria. A self-controlled risk-interval design was applied with an ‘at-risk period’ defined as the two-year period after and the ‘control period’, defined as the two-year before treatment. The hazard ratio (HR) was calculated using a fixed-effect proportional hazards model. ResultsOf the 2854 patients, 1640 (57.5%) were men; the mean age was 64 ± 13 years. The risk for VTE was 7.4% at 6 months and 13.8% at 1 year after starting an ICI. The rate of VTE was > 4-fold higher after starting an ICI (HR 4.98, 95% CI 3.65–8.59, p < 0.001). There was a 5.7-fold higher risk for deep vein thrombosis (HR 5.70, 95% CI 3.79–8.59, p < 0.001) and a 4.75-fold higher risk for pulmonary embolism (HR 4.75, 95% CI 3.20–7.10, p < 0.001). Comparing patients with and without a VTE event, a history of melanoma and older age predicted lower risk of VTE, while a higher Khorana risk score, history of hypertension and history of VTE predicted higher risk. ConclusionsThe rate of VTE among patients on an ICI is high and increases after starting an ICI.

Association between Influenza Vaccination and the Risk of Bell's Palsy in the Korean Elderly.

Previous studies have shown controversial results on the risk of Bell’s palsy after influenza vaccination. Since the antigenic components of influenza vaccine can vary from season to season, continuous safety monitoring is required. The aim of the present study was to determine whether there was an increased risk of Bell’s palsy in the elderly after influenza vaccination between the 2015/2016 and 2017/2018 flu seasons. This study included the elderly who received influenza vaccinations for three flu seasons using a large-linked database of vaccination registration data from the Korea Disease Control and Prevention Agency and the National Health Insurance Service claims data. We used a self-controlled risk interval design with a risk interval of 1 to 42 days and a control interval of 57 to 98 days postvaccination and calculated the incidence rate ratio. To ensure the robustness of the results, sensitivity analyses were also carried out with different risk and control intervals. Of 4,653,440 elderly people who received the influenza vaccine, there was no statistically significant increase in the risk of Bell’s palsy (IRR: 0.99, 95% CI: 0.92–1.07). Similar results were found in analysis results for each season and the results of the sensitivity analyses excluding the 2017/2018 season. In conclusion, we found no evidence of an increased risk of Bell’s palsy after influenza vaccination. The results of our study provide reassurance about the safety of the influenza vaccine NIP program. However, it is necessary to continuously monitor the risk of Bell’s palsy during future flu seasons.

Association between human papillomavirus vaccination and serious adverse events in South Korean adolescent girls: nationwide cohort study

Objective To evaluate the association between human papillomavirus (HPV) vaccination and serious adverse events in adolescent girls in South Korea. Design Cohort study. Setting A large linked database created by...

5. Observational Study of Routine Use of 9-Valent Human Papillomavirus Vaccine: Safe in More Than 140,000 Individuals

BackgroundNine-valent human papillomavirus (HPV) vaccine (9vHPV vaccine, Gardasil®9) was licensed in the US in Dec-2014. Using a self-controlled risk interval design, we conducted a post-licensure retrospective cohort study within Kaiser Permanente in Northern California (KPNC) to assess 9vHPV safety following routine administration.MethodsWe included KPNC members 9-years or older who received 9vHPV as their first dose of HPV vaccine between Oct-2015 and Sep-2017. Post-vaccination emergency and hospitalization events were compared during risk intervals (days 1–60 and 0–14) with later self-comparison intervals using conditional logistic regression, following all 9vHPV vaccine doses combined, and by dose. We investigated significant findings by assessing post-vaccination timing and medical record reviews. We evaluated and reviewed medical records for all day 0 allergic reaction and syncope events, and all deaths during the study. An independent Safety Review Committee reviewed potential safety signals.ResultsWe studied 140,628 9vHPV-vaccinated individuals, including 69,027 (49%) who received 2 doses and 29,901 (21%) 3 doses, totaling 239,556 doses. Eight categories were significantly increased in at least one analysis (Table). On review, most findings were previously known, preceded vaccination, or were better explained by other medical history. Some day 0 allergic reactions and syncope were potentially related to vaccination. None of the 20 deaths were considered related to 9vHPV.Table. Elevated diagnosis categories comparing risk and self-comparison intervals.Diagnosis CategoriesORs (95% CI)Diabetes mellitus1.66 (1.01, 2.74)DeliriumNE (1.11, NE)Nervous system disorders+21.33 (1.02, 1.72)Digestive disorders+41.21 (1.03, 1.41)Male genital disease1.60 (1.04, 2.46)Skin disorders+11.88 (1.00, 3.53)Congenital anomalies, nervous system5.01 (1.10, 22.83)Symptoms, ill-defined+11.36 (1.13, 1.64) +n indicates number of elevated sub-categories, for a total of 16 categories. NE: not estimable.ConclusionThis large study of individuals who received only 9vHPV vaccine did not identify any new safety events related to 9vHPV administration and provides reassuring evidence of the favorable safety profile of the 9vHPV vaccine.DisclosuresSe Li, PhD, Merck & Co., Inc. (Employee, Shareholder) Christine Velicer, PhD, Merck & Co., Inc. (Employee, Shareholder) Patricia Saddier, MD, PhD, Merck & Co., Inc. (Employee, Shareholder) Nicola P. Klein, MD, PhD, GSK group of companies (Research Grant or Support)Merck (Grant/Research Support)Pfizer (Grant/Research Support)Protein Science (now SP) (Grant/Research Support)Sanofi Pasteur (Grant/Research Support)

Assessment of pre-specified adverse events following varicella vaccine: A population-based self-controlled risk interval study

BackgroundClinical trials and spontaneous reporting systems have revealed rare but biologically plausible adverse events following varicella immunization. Few post-marketing controlled studies have been conducted to assess the relationship between the varicella vaccine and these outcomes. ObjectivesTo evaluate the risk of pneumonia, idiopathic thrombocytopenic purpura (ITP), meningitis, encephalitis and ischemic stroke following varicella immunization. Materials and methodsThis nationwide observational study was based on Taiwan National Health Insurance data and National Immunization Information System from 2004 through 2014. Primary analysis included children aged 12–35 months who received the single varicella vaccine on the date of administration. The self-controlled risk interval design compared the incidence of pre-specified outcomes during a risk interval of 1–42 days post-vaccination and a control interval of 43–84 days. The outcomes of interest were defined as admitted pneumonia, ITP, meningitis, encephalitis, and ischemic stroke, as well as fracture as a negative control. Conditional Poisson regression was used to assess the incidence rate ratio (aIRR) with adjustments for age and seasonal effects. ResultsAmong 1,194,189 children, who receiving the varicella vaccine, there was no observed increase in the risk for ITP (aIRR 1.00; 95% CI, 0.76–1.33), meningitis (aIRR 1.21; 95% CI, 0.49–2.95), encephalitis (aIRR 1.00; 95% CI, 0.62–1.60), or ischemic stroke (aIRR 1.24; 95% CI, 0.31–4.95). A clustering feature with pneumonia occurred during days 36–42 post-vaccination (aIRR 1.10; 95% CI, 1.02–1.18). An increase in the risk for ITP was observed in children receiving the varicella and MMR vaccines concomitantly (aIRR 1.70; 95% CI, 1.19–2.43), but not among those receiving the varicella vaccine only. ConclusionsWe detected a small risk of incidental pneumonia associated with varicella vaccine in the 6th week after immunization. There was no increase in the risk of other pre-specified adverse events.

The risk of febrile seizures following influenza and 13-valent pneumococcal conjugate vaccines

BackgroundEvidence on the risk of febrile seizures after inactivated influenza vaccine (IIV) and 13-valent pneumococcal conjugate vaccine (PCV13) is mixed. In the FDA-sponsored Sentinel Initiative, we examined risk of febrile seizures after IIV and PCV13 in children 6–23 months of age during the 2013–14 and 2014–15 influenza seasons. MethodsUsing claims data and a self-controlled risk interval design, we compared the febrile seizure rate in a risk interval (0–1 days) versus control interval (14–20 days). In exploratory analyses, we assessed whether the effect of IIV was modified by concomitant PCV13 administration. ResultsAdjusted for age, calendar time and concomitant administration of the other vaccine, the incidence rate ratio (IRR) for risk of febrile seizures following IIV was 1.12 (95% CI 0.80, 1.56) and following PCV13 was 1.80 (95% CI 1.29, 2.52). The attributable risk for febrile seizures following PCV13 ranged from 0.33 to 5.16 per 100,000 doses by week of age.The age and calendar-time adjusted IRR comparing exposed to unexposed time was numerically larger for concomitant IIV and PCV13 (IRR 2.80, 95% CI 1.63, 4.83), as compared to PCV13 without concomitant IIV (IRR 1.54, 95% CI 1.04, 2.28), and the IRR for IIV without concomitant PCV13 suggested no independent effects of IIV (IRR 0.94, 95% CI 0.63, 1.42). Taken together, this suggests a possible interaction between IIV and PCV13, though our study was not sufficiently powered to provide a precise estimate of the interaction. ConclusionsWe found an elevated risk of febrile seizures after PCV13 vaccine but not after IIV. The risk of febrile seizures after PCV13 is low compared to the overall risk in this population of children, and the risk should be interpreted in the context of the importance of preventing pneumococcal infections.

Kawasaki disease and 13-valent pneumococcal conjugate vaccination among young children: A self-controlled risk interval and cohort study with null results.

BackgroundKawasaki disease is an acute vasculitis that primarily affects children younger than 5 years of age. Its etiology is unknown. The United States Vaccine Safety Datalink conducted postlicensure safety surveillance for 13-valent pneumococcal conjugate vaccine (PCV13), comparing the risk of Kawasaki disease within 28 days of PCV13 vaccination with the historical risk after 7-valent PCV (PCV7) vaccination and using chart-validation. A relative risk (RR) of 2.38 (95% CI 0.92–6.38) was found. Concurrently, the Food and Drug Administration (FDA) conducted a postlicensure safety review that identified cases of Kawasaki disease through adverse event reporting. The FDA decided to initiate a larger study of Kawasaki disease risk following PCV13 vaccination in the claims-based Sentinel/Postlicensure Rapid Immunization Safety Monitoring (PRISM) surveillance system. The objective of this study was to determine the existence and magnitude of any increased risk of Kawasaki disease in the 28 days following PCV13 vaccination.Methods and findingsThe study population included mostly commercially insured children from birth to <24 months of age in 2010 to 2015 from across the US. Using claims data of participating Sentinel/PRISM data-providing organizations, PCV13 vaccinations were identified by means of current procedural terminology (CPT), Healthcare Common Procedure Coding System (HCPCS), and National Drug Code (NDC) codes. Potential cases of Kawasaki disease were identified by first-in-365-days International Classification of Diseases 9th revision (ICD-9) code 446.1 or International Classification of Diseases 10th revision (ICD-10) code M30.3 in the inpatient setting. Medical records were sought for potential cases and adjudicated by board-certified pediatricians. The primary analysis used chart-confirmed cases with adjudicated symptom onset in a self-controlled risk interval (SCRI) design, which controls for time-invariant potential confounders. The prespecified risk interval was Days 1–28 after vaccination; a 28-day-long control interval followed this risk interval. A secondary analytic approach used a cohort design, with alternative potential risk intervals of Days 1–28 and Days 1–42. The varying background risk of Kawasaki disease by age was adjusted for in both designs. In the primary analysis, there were 43 confirmed cases of Kawasaki disease in the risk interval and 44 in the control interval. The age-adjusted risk estimate was 1.07 (95% CI 0.70–1.63; p = 0.76). In the secondary, cohort analyses, which included roughly 700 potential cases and more than 3 million person-years, the risk estimates of potential Kawasaki disease in the risk interval versus in unexposed person-time were 0.84 (95% CI 0.65–1.08; p = 0.18) for the Days 1–28 risk interval and 0.97 (95% CI 0.79–1.19; p = 0.80) for the Days 1–42 risk interval. The main limitation of the study was that we lacked the resources to conduct medical record review for all the potential cases of Kawasaki disease. As a result, potential cases rather than chart-confirmed cases were used in the cohort analyses.ConclusionsWith more than 6 million doses of PCV13 administered, no evidence was found of an association between PCV13 vaccination and Kawasaki disease onset in the 4 weeks after vaccination nor of an elevated risk extending or concentrated somewhat beyond 4 weeks. These null results were consistent across alternative designs, age-adjustment methods, control intervals, and categories of Kawasaki disease case included.

Use of FDA's Sentinel System to Quantify Seizure Risk Immediately Following New Ranolazine Exposure.

Neurological complications including seizures have been reported with ranolazine. We sought to quantify the risk of seizure-related hospitalizations or emergency department events following ranolazine exposure in the Sentinel System (2006-2015). Eligibility criteria were new use of ranolazine after 183days washout period and absence of seizure diagnoses, anti-epileptic drugs, or seizure-related disorders during the baseline period. Among 52,155 ranolazine users, we identified 28 seizures in the 1-32days after new ranolazine dispensing: 12 occurring in days 1-10 (high-risk window), 11 in days 11-20 (moderate-risk window) and 5 in the control window (days 21-32). Assuming an equal likelihood of seizure events across the 32-day observation window, we estimate an attributable risk of 0.9 excess cases per 10,000 exposed users. Using a self-controlled risk interval design with exact logistic regression, seizures were elevated in the high-risk window (relative risk [RR] 2.88 (95% confidence interval [CI] 1.01-8.33) compared with the control window. No significant increased risk was observed in the moderate window. Half of the seizure cases had a diagnosis of renal disease, although seizure risk was not significant (RR 3.20 [CI 0.82-14.01]). A majority of patients in both risk windows were 75years or older. Our study suggests risk among younger ranolazine patients is rare. Given the imprecision of the risk estimates, we interpret the elevated seizure risk following ranolazine exposure with caution. Further analysis in a larger elderly population is warranted.

Risk interval analysis of emergency room visits following colonoscopy in patients with inflammatory bowel disease.

Background and aimsPrior studies suggest that colonoscopy may exacerbate inflammatory bowel disease (IBD) symptoms. Thus, our study aimed to determine risk of emergency room (ER) visits associated with colonoscopy among IBD patients and evaluate potential modifiers of this risk.MethodsThe study population included IBD patients in the Multi-Payer Claims Database who were >20 years old and had a colonoscopy from 2007–2010. We used a self-controlled risk interval design and mixed-effects Poisson regression models to calculate risk ratios (RR) and 95% confidence intervals (CI) comparing the incidence of ER visits in the 1–4 weeks following colonoscopy (risk interval) to the incidence of ER visits in the 7–10 weeks after colonoscopy (control interval). We also conducted stratified analyses by patient characteristics, bowel preparation type, and medication.ResultsThere were 212,205 IBD patients with at least 1 colonoscopy from 2007–2010, and 3,699 had an ER visit during the risk and/or control interval. The risk of an ER visit was higher in the 4-week risk interval following colonoscopy compared to the control interval (RR = 1.24; 95% CI: 1.17–1.32). The effect was strongest in those <41 years old (RR = 1.60; 95% CI: 1.21–2.11), in women (RR = 1.32; 95% CI: 1.21–1.44), and in those with sodium phosphate bowel preparation (RR = 2.09; 95% CI: 1.02–4.29). Patients using immunomodulators had no increased risk of ER visits (RR = 0.75; 95% CI: 0.35–1.59).ConclusionsOur results suggest that there is an increased risk of ER visits following colonoscopy among IBD patients, but that immunomodulators and mild bowel preparation agents may mitigate this risk.

2461. Safety of Quadrivalent Meningococcal Polysaccharide Diphtheria Toxoid-Conjugate Vaccine in Adolescents

BackgroundThe first quadrivalent meningococcal conjugate vaccine (MenACWY-D) was recommended for use in adolescents in 2005. Soon after, case reports of Guillain-Barre syndrome (GBS) following vaccination prompted subsequent studies, with a meta-analysis concluding that the attributable risk of GBS after MenACWY-D is unlikely to exceed 1 case per million vaccinations. We conducted a retrospective cohort study in the Vaccine Safety Datalink to assess the risk of 10 outcomes, including GBS, following MenACWY-D.MethodsWe included adolescents (aged 11–18 years) vaccinated with MenACWY-D during the years 2005–2014. We identified pre-specified outcomes using ICD-9 (International Classification of Disease, version 9) codes. We used automated data only for Bell’s palsy, fever, seizure and syncope, and we confirmed incident cases by medical record review for acute disseminated encephalomyelitis (ADEM), acute transverse myelitis (ATM), anaphylaxis, chronic inflammatory demyelinating polyneuropathy (CIDP), GBS and Henoch-Schönlein purpura (HSP). We used a self-controlled risk interval design to estimate relative risk (RR).ResultsFollowing 1.4 million doses of MenACWY-D, we detected increased risks for fever in the 1–6 days following vaccination (RR 1.5, 95% confidence interval [CI] 1.3–1.7) and syncope on the day of vaccination (RR 5.8, 95% CI 4.1–8.3), but not for seizures (RR 1.1, 95% CI 0.7–1.9) or Bell’s palsy (RR 1.1, 95% CI 0.8–1.5). We detected no cases in the post-vaccination risk intervals for CIDP, ADEM or ATM. We detected few cases of the other outcomes resulting in relatively unstable RR estimates: anaphylaxis (RR 1.9, 95% CI 0.5–7.1), GBS (RR 2.5, 95% CI 0.6–10.0) and HSP (RR 1.6, 95% CI 0.7–3.3). We estimated that the attributable risk of GBS was 1.5 cases per million vaccinations (upper bound of one-sided 95% CI, 4.9).ConclusionIn a large retrospective cohort, we detected increased risks for syncope and fever, but not seizures or Bell’s palsy, following vaccination with MenACWY-D. Other outcomes were rare. Our findings, consistent with previous studies, suggest that the increased risk of GBS, if any, is likely small (<5 excess cases of GBS per million vaccinations).Disclosures N. P. Klein, Sanofi Pasteur: Investigator, Research grant. Merck: Investigator, Research grant. GSK: Investigator, Research grant. Pfizer: Investigator, Research support. Protein Science: Investigator, Research grant. MedImmune: Investigator, Research grant. Dynavax: Research Contractor, Grant recipient. M. L. Jackson, Novartis: Grant Investigator, Research support.

Self-controlled case series studies: Just how rare does a rare non-recurrent outcome need to be?

The self-controlled case series method assumes that adverse outcomes arise according to a non-homogeneous Poisson process. This implies that it is applicable to independent recurrent outcomes. However, the self-controlled case series method may also be applied to unique, non-recurrent outcomes or first outcomes only, in the limit where these become rare. We investigate this rare outcome assumption when the self-controlled case series method is applied to non-recurrent outcomes. We study this requirement analytically and by simulation, and quantify what is meant by 'rare' in this context. In simulations we also apply the self-controlled risk interval design, a special case of the self-controlled case series design. To illustrate, we extract data on the incidence rate of some recurrent and non-recurrent outcomes within a defined study population to check whether outcomes are sufficiently rare for the rare outcome assumption to hold when applying the self-controlled case series method to first or unique outcomes. The main findings are that the relative bias should be no more than 5% when the cumulative incidence over total time observed is less than 0.1 per individual. Inclusion of age (or calendar time) effects will further reduce bias. Designs that begin observation with exposure maximise bias, whereas little or no bias will be apparent when there is no time trend in the distribution of exposures, or when exposure is central within time observed.