Vaccine Effectiveness Estimates Research Articles

Vaccine effectiveness against emerging COVID-19 variants using digital health data

BackgroundParticipatory surveillance of self-reported symptoms and vaccination status can be used to supplement traditional public health surveillance and provide insights into vaccine effectiveness and changes in the symptoms produced by an infectious disease. The University of Maryland COVID Trends and Impact Survey provides an example of participatory surveillance that leveraged Facebook’s active user base to provide self-reported symptom and vaccination data in near real-time.MethodsHere, we develop a methodology for identifying changes in vaccine effectiveness and COVID-19 symptomatology using the University of Maryland COVID Trends and Impact Survey data from three middle-income countries (Guatemala, Mexico, and South Africa). We implement conditional logistic regression to develop estimates of vaccine effectiveness conditioned on the prevalence of various definitions of self-reported COVID-like illness in lieu of confirmed diagnostic test results.ResultsWe highlight a reduction in vaccine effectiveness during Omicron-dominated waves of infections when compared to periods dominated by the Delta variant (median change across COVID-like illness definitions: −0.40, IQR[−0.45, −0.35]. Further, we identify a shift in COVID-19 symptomatology towards upper respiratory type symptoms (i.e., cough and sore throat) during Omicron periods of infections. Stratifying COVID-like illness by the National Institutes of Health’s (NIH) description of mild and severe COVID-19 symptoms reveals a similar level of vaccine protection across different levels of COVID-19 severity during the Omicron period.ConclusionsParticipatory surveillance data alongside methodologies described in this study are particularly useful for resource-constrained settings where diagnostic testing results may be delayed or limited.

A combined cross-sectional analysis and case-control study evaluating tick-borne encephalitis vaccination coverage, disease and vaccine effectiveness in children and adolescents, Switzerland, 2005 to 2022.

BackgroundTick-borne encephalitis (TBE) is a severe, vaccine-preventable viral infection of the central nervous system. Symptoms are generally milder in children and adolescents than in adults, though severe disease does occur. A better understanding of the disease burden and duration of vaccine-mediated protection is important for vaccination recommendations.AimTo estimate TBE vaccination coverage, disease severity and vaccine effectiveness (VE) among individuals aged 0-17 years in Switzerland.MethodsVaccination coverage between 2005 and 2022 was estimated using the Swiss National Vaccination Coverage Survey (SNVCS), a nationwide, repeated cross-sectional study assessing vaccine uptake. Incidence and severity of TBE between 2005 and 2022 were determined using data from the Swiss disease surveillance system and VE was calculated using a case-control analysis, matching TBE cases with SNVCS controls.ResultsOver the study period, vaccination coverage increased substantially, from 4.8% (95% confidence interval (CI): 4.1-5.5%) to 50.1% (95% CI: 48.3-52.0%). Reported clinical symptoms in TBE cases were similar irrespective of age. Neurological involvement was less likely in incompletely (1-2 doses) and completely (≥ 3 doses) vaccinated cases compared with unvaccinated ones. For incomplete vaccination, VE was 66.2% (95% CI: 42.3-80.2), whereas VE for complete vaccination was 90.8% (95% CI: 87.7-96.4). Vaccine effectiveness remained high, 83.9% (95% CI: 69.0-91.7) up to 10 years since last vaccination.ConclusionsEven children younger than 5 years can experience severe TBE. Incomplete and complete vaccination protect against neurological manifestations of the disease. Complete vaccination offers durable protection up to 10 years against TBE.

End of 2022/23 Season Influenza Vaccine Effectiveness in Primary Care in Great Britain.

The 2022/23 influenza season in the United Kingdom saw the return of influenza to prepandemic levels following two seasons with low influenza activity. The early season was dominated by A(H3N2), with cocirculation of A(H1N1), reaching a peak late December 2022, while influenza B circulated at low levels during the latter part of the season. From September to March 2022/23, influenza vaccines were offered, free of charge, to all aged 2-13 (and 14-15 in Scotland and Wales), adults up to 49 years of age with clinical risk conditions and adults aged 50 and above across the mainland United Kingdom. End-of-season adjusted vaccine effectiveness (VE) estimates against sentinel primary-care attendance for influenza-like illness, where influenza infection was laboratory confirmed, were calculated using the test negative design, adjusting for potential confounders. Results In the mainland United Kingdom, end-of-season VE against all laboratory-confirmed influenza for all those > 65 years of age, most of whom received adjuvanted quadrivalent vaccines, was 30% (95% CI: -6% to 54%). VE for those aged 18-64, who largely received cell-based vaccines, was 47% (95% CI: 37%-56%). Overall VE for 2-17 year olds, predominantly receiving live attenuated vaccines, was 66% (95% CI: 53%-76%). The paper provides evidence of moderate influenza VE in 2022/23.

Exploring the effect of clinical case definitions on influenza vaccine effectiveness estimation at primary care level: Results from the end-of-season 2022–23 VEBIS multicentre study in Europe

BackgroundWithin influenza vaccine effectiveness (VE) studies at primary care level with a laboratory-confirmed outcome, clinical case definitions for recruitment of patients can vary. We used the 2022–23 VEBIS primary care European multicentre study end-of-season data to evaluate whether the clinical case definition affected IVE estimates. MethodsWe estimated VE using a multicentre test-negative case-control design. We measured VE against any influenza and influenza (sub)types, by age group (0–14, 15–64, ≥65 years) and by influenza vaccine target group, using logistic regression. We estimated IVE among patients meeting the European Union (EU) acute respiratory infection (ARI) case definition and among those meeting the EU influenza-like illness (ILI) case definition, including only sites providing information on specific symptoms and recruiting patients using an ARI case definition (as the EU ILI case definition is a subset of the EU ARI one). ResultsWe included 24 319 patients meeting the EU ARI case definition, of whom 21 804 patients (90 %) meet the EU ILI case definition, for the overall pooled VE analysis against any influenza. The overall and influenza (sub)type-specific VE varied by ≤2 % between EU ILI and EU ARI populations. DiscussionAmong all analyses, we found similar VE estimates between the EU ILI and EU ARI populations, with few (10%) additional non-ILI ARI patients recruited. These results indicate that VE in the 2022–23 influenza season was not affected by use of a different clinical case definition for recruitment, although we recommend investigating whether this holds true for next seasons.

Effectiveness of BNT162b2 COVID-19 primary series vaccination in children aged 5–17 years in the United States: a cohort study

BackgroundCOVID-19 vaccines are authorized for use in children in the United States; real-world assessment of vaccine effectiveness in children is needed. This study’s objective was to estimate the effectiveness of receiving a complete primary series of monovalent BNT162b2 (Pfizer-BioNTech) COVID-19 vaccine in US children.MethodsThis cohort study identified children aged 5–17 years vaccinated with BNT162b2 matched with unvaccinated children. Participants and BNT162b2 vaccinations were identified in Optum and CVS Health insurance administrative claims databases linked with Immunization Information System (IIS) COVID-19 vaccination records from 16 US jurisdictions between December 11, 2020, and May 31, 2022 (end date varied by database and IIS). Vaccinated children were followed from their first BNT162b2 dose and matched to unvaccinated children on calendar date, US county of residence, and demographic and clinical factors. Censoring occurred if vaccinated children failed to receive a timely dose 2 or if unvaccinated children received any dose. Two COVID-19 outcome definitions were evaluated: COVID-19 diagnosis in any medical setting and COVID-19 diagnosis in hospitals/emergency departments (EDs). Propensity score-weighted hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated with Cox proportional hazards models, and vaccine effectiveness (VE) was estimated as 1 minus HR. VE was estimated overall, within age subgroups, and within variant-specific eras. Sensitivity, negative control, and quantitative bias analyses evaluated various potential biases.ResultsThere were 453,655 eligible vaccinated children one-to-one matched to unvaccinated comparators (mean age 12 years; 50% female). COVID-19 hospitalizations/ED visits were rare in children, regardless of vaccination status (Optum, 41.2 per 10,000 person-years; CVS Health, 44.1 per 10,000 person-years). Overall, vaccination was associated with reduced incidence of any medically diagnosed COVID-19 (meta-analyzed VE = 38% [95% CI, 36–40%]) and hospital/ED–diagnosed COVID-19 (meta-analyzed VE = 61% [95% CI, 56–65%]). VE estimates were lowest among children 5–11 years and during the Omicron-variant era.ConclusionsReceipt of a complete BNT162b2 vaccine primary series was associated with overall reduced medically diagnosed COVID-19 and hospital/ED–diagnosed COVID-19 in children; observed VE estimates differed by age group and variant era.RegistrationThe study protocol was publicly posted on the BEST Initiative website (https://bestinitiative.org/wp-content/uploads/2022/03/C19-VX-Effectiveness-Protocol_2022_508.pdf).

[Analysis Of Data Quality/Completeness In Covid-19 Cases: Why A Digital Integrated Data Collection Is Also Necessary For Pandemic Control].

Epidemiological data on the corona pandemic collected in the public health sector in Germany have been less useful in estimating vaccine effectiveness and clinical outcomes compared to other countries. In this retrospective observational study, we examined the completeness of selected own data collected during the pandemic. Information on the important parameters of hospitalization, vaccination status and risk factors for severe course and death over different periods were considered and evaluated descriptively. The data are discussed in the extended context of required digital strategies in Germany. From January 1, 2022 to June 30, 2022, we found 126,920 administrative procedures related to COVID-19. With regard to the data on hospitalization, in 19,749 cases, it was stated "No", in 1,990 cases "Yes" and in 105,181 cases (83+%) "Not collected" or "Not ascertainable". Concerning vaccinations, only a small proportion of procedures contained information on the type of vaccine (11.1+%), number of vaccinations (4.4+%) and date of the last vaccination (2.1+%). The completeness of data on chronic conditions/risk factors in COVID-19-related deaths decreased over four consecutive periods between 2020 and 2022 as case numbers increased. Future strategies taking into account meaningfulness and completeness of data must comprise modern technical solutions with digital data collection on infections without putting the principle of data protection at risk.

Estimates of Seasonal Influenza Burden That Could Be Averted by Improved Influenza Vaccines in the Australian Population Aged Under 65 Years, 2015-2019.

The interpretation of relative vaccine effectiveness (rVE) of improved influenza vaccines is complex. Estimation of burden averted is useful to contextualise their potential impact across different seasons. For the population aged under 65 years in Australia, this study estimated the additional morbidity and mortality that could be averted using improved influenza vaccines. We used observed, season-specific (2015-2019) influenza notification and influenza-coded hospitalisation frequencies and published modelled estimates of influenza-associated hospitalisations and deaths that occurred under the prevailing influenza vaccination coverage scenario. After back-calculating to the estimated burden in the population without vaccination, we applied published standard influenza vaccine effectiveness and coverage estimates to calculate the burden potentially averted by standard and improved influenza vaccines. A plausible range of rVE values were used, assuming 50% coverage. The percentage point difference in absolute vaccine effectiveness (VE) of an improved vaccine compared to a standard vaccine is directly proportional to its rVE and inversely proportional to the effectiveness of the standard vaccine. The incremental burden averted by an improved vaccine is a function of both its difference in absolute VE and the severity of the influenza season. Assuming an rVE of 15% with 50% coverage, the improved vaccine was estimated to additionally avert 1517 to 12,641 influenza notifications, 287 to 1311 influenza-coded hospitalisations and 9 to 33 modelled all-cause influenza deaths per year compared to the standard vaccine. Improved vaccines can have substantial clinical and population impact, particularly when the effectiveness of standard vaccines is low, and burden is high.

[Effectiveness of COVID-19 mRNA vaccine against hospitalization during the alpha and delta variant surges in Tokyo].

Objective　Evidence on COVID-19 vaccine effectiveness outside of clinical trials is insufficient. We aimed to determine the real-world effectiveness of mRNA vaccines in preventing hospitalization via data from the Health Center Real-time Information-sharing System on COVID-19 (HER-SYS), a national public database on COVID-19 cases in Japan.Methods　This case-control study targeted residents of Minato-ward, Tokyo, aged ≥50 years, who were COVID-19 positive between May 17 and Sep 30, 2021 (the alpha and delta strains-dominant period). Those hospitalized within 10 days of onset or diagnosis were considered the case group and control patients were not hospitalized. Patients were grouped according to vaccination status; group 1, unvaccinated, groups 2 and 3, who received the first dose ≤14 days and ≥15 days, respectively, and groups 4 and 5, who received the second dose ≤14 and ≥15 days before onset, respectively. To estimate vaccine effectiveness, adjusted odd ratios (OR) were calculated for each group against group 1. Furthermore, to determine other risk factors for hospitalization, OR were calculated for age, sex, and presence of any underlying diseases.Results　This study analyzed 192 case and 366 control patients. The adjusted OR were 1.48 (95% Cl=0.88-2.50), 0.71 (95% Cl=0.27-1.80), 0.58 (95% Cl=0.20-1.66), and 0.30 (95% Cl=0.13-0.67) for groups 2-5, respectively. Additionally, the adjusted OR were 1.57 (95% Cl=1.07-2.29), 1.05 (95% Cl=1.03-1.07), and 1.69 (95% Cl=1.15-2.48) for presence of underlying disease, 1-year increase of age, and men, respectively.Conclusion　Patients aged ≥50 years who received the second dose of the mRNA vaccine ≥15 days before onset had a significantly lower risk of hospitalization. Additionally, older age, men, and presence of underlying diseases were risk factors for hospitalization. Further studies on vaccine effectiveness to prevent severe diseases, hospitalization, and death following booster immunization during the omicron strain-dominant period are warranted.

Predicting Vaccine Effectiveness for Hospitalization and Symptomatic Disease for Novel SARS-CoV-2 Variants Using Neutralizing Antibody Titers.

The emergence of new virus variants, including the Omicron variant (B.1.1.529) of SARS-CoV-2, can lead to reduced vaccine effectiveness (VE) and the need for new vaccines or vaccine doses if the extent of immune evasion is severe. Neutralizing antibody titers have been shown to be a correlate of protection for SARS-CoV-2 and other pathogens, and could be used to quickly estimate vaccine effectiveness for new variants. However, no model currently exists to provide precise VE estimates for a new variant against severe disease for SARS-CoV-2 using robust datasets from several populations. We developed predictive models for VE against COVID-19 symptomatic disease and hospitalization across a 54-fold range of mean neutralizing antibody titers. For two mRNA vaccines (mRNA-1273, BNT162b2), models fit without Omicron data predicted that infection with the BA.1 Omicron variant increased the risk of hospitalization 2.8-4.4-fold and increased the risk of symptomatic disease 1.7-4.2-fold compared to the Delta variant. Out-of-sample validation showed that model predictions were accurate; all predictions were within 10% of observed VE estimates and fell within the model prediction intervals. Predictive models using neutralizing antibody titers can provide rapid VE estimates, which can inform vaccine booster timing, vaccine design, and vaccine selection for new virus variants.

Evaluation of Two Vaccines against Foot-and-Mouth Disease Used in Transcaucasian Countries by Small-Scale Immunogenicity Studies Conducted in Georgia, Azerbaijan and Armenia.

In countries endemic for foot-and-mouth disease (FMD), routine or emergency vaccinations are strategic tools to control the infection. According to the WOAH/FAO guidelines, a prior estimation of vaccine effectiveness is recommendable to optimize control programs. This study reports the results of a small-scale immunogenicity study performed in Transcaucasian Countries. Polyvalent vaccines, including FMDV serotypes O, A (two topotypes) and Asia1 from two different manufacturers, were evaluated in Georgia, Azerbaijan and Armenia. Naïve large and small ruminants were vaccinated once and a subgroup received a second booster dose. The titers of neutralizing antibodies in sera collected sequentially up to 180 DPV were determined through the Virus Neutralization Test versus homologous strains. This study led to the estimate that both the vaccines evaluated will not induce a protective and long-lasting population immunity, even after a second vaccination, stressing that consecutive administrations of both vaccines every three months are mandatory if one aspires to achieve protective herd immunity.

Effectiveness of the 2023-2024 Formulation of the Coronavirus Disease 2019 mRNA Vaccine.

The purpose of this study was to evaluate whether the 2023-2024 formulation of the COVID-19 mRNA vaccine protects against COVID-19. Employees of Cleveland Clinic in employment when the 2023-2024 formulation of the COVID-19 mRNA vaccine became available to employees, were included. Cumulative incidence of COVID-19 over the following 17 weeks was examined prospectively. Protection provided by vaccination (analyzed as a time-dependent covariate) was evaluated using Cox proportional hazards regression, with time-dependent coefficients used to separate effects before and after the JN.1 lineage became dominant. The analysis was adjusted for the propensity to get tested, age, sex, pandemic phase when the last prior COVID-19 episode occurred, and the number of prior vaccine doses. Among 48210 employees, COVID-19 occurred in 2462 (5.1%) during the 17 weeks of observation. In multivariable analysis, the 2023-2024 formula vaccinated state was associated with a significantly lower risk of COVID-19 before the JN.1 lineage became dominant (HR, .58; 95% C.I., .49-.68, p-value < .001), and lower risk but one that did not reach statistical significance after (HR, .81; 95% C.I., .65-1.01, p-value 0.06). Estimated vaccine effectiveness (VE) was 42% (95% C.I., 32%-51%) before the JN.1 lineage became dominant, and 19% (C.I., -1%-35%) after. Risk of COVID-19 was lower among those previously infected with an XBB or more recent lineage, and increased with the number of vaccine doses previously received. The 2023-2024 formula COVID-19 vaccine given to working-aged adults afforded modest protection overall against COVID-19 before the JN.1 lineage became dominant, and less protection after.

Vaccine Effectiveness Against Long COVID in Children.

Vaccination reduces the risk of acute coronavirus disease 2019 (COVID-19) in children, but it is less clear whether it protects against long COVID. We estimated vaccine effectiveness (VE) against long COVID in children aged 5 to 17 years. This retrospective cohort study used data from 17 health systems in the RECOVER PCORnet electronic health record program for visits after vaccine availability. We examined both probable (symptom-based) and diagnosed long COVID after vaccination. The vaccination rate was 67% in the cohort of 1 037 936 children. The incidence of probable long COVID was 4.5% among patients with COVID-19, whereas diagnosed long COVID was 0.8%. Adjusted vaccine effectiveness within 12 months was 35.4% (95 CI 24.5-44.7) against probable long COVID and 41.7% (15.0-60.0) against diagnosed long COVID. VE was higher for adolescents (50.3% [36.6-61.0]) than children aged 5 to 11 (23.8% [4.9-39.0]). VE was higher at 6 months (61.4% [51.0-69.6]) but decreased to 10.6% (-26.8% to 37.0%) at 18-months. This large retrospective study shows moderate protective effect of severe acute respiratory coronavirus 2 vaccination against long COVID. The effect is stronger in adolescents, who have higher risk of long COVID, and wanes over time. Understanding VE mechanism against long COVID requires more study, including electronic health record sources and prospective data.

Waning effectiveness of mRNA COVID-19 vaccines against inpatient and emergency department encounters.

In the United States, most real-world estimates of COVID-19 vaccine effectiveness are based on data drawn from large health systems or sentinel populations. More data is needed to understand how the benefits of vaccination may vary across US populations with disparate risk profiles and policy contexts. We aimed to provide estimates of mRNA COVID-19 vaccine effectiveness against moderate and severe outcomes of COVID-19 based on state population-level data sources. Using statewide integrated administrative and clinical data and a test-negative case-control study design, we assessed mRNA COVID-19 vaccine effectiveness against SARS-CoV-2-related hospitalizations and emergency department visits among adults in South Carolina. We presented estimates of vaccine effectiveness at discrete time intervals for adults who received one, two or three doses of mRNA COVID-19 vaccine compared to adults who were unvaccinated. We also evaluated changes in vaccine effectiveness over time (waning) for the overall sample and in subgroups defined by age. We showed that while two doses of mRNA COVID-19 vaccine were initially highly effective, vaccine effectiveness waned as time elapsed since the second dose. Compared to protection against hospitalizations, protection against emergency department visits was found to wane more sharply. In all cases, a third dose of mRNA COVID-19 vaccine conferred significant gains in protection relative to waning protection after two doses. Further, over more than 120 days of follow-up, the data revealed relatively limited waning of vaccine effectiveness after a third dose of mRNA COVID-19 vaccine.

Effectiveness of Omicron XBB.1.5 vaccine against infection with SARS-CoV-2 Omicron XBB and JN.1 variants, prospective cohort study, the Netherlands, October 2023 to January 2024.

We estimated vaccine effectiveness (VE) of SARS-CoV-2 Omicron XBB.1.5 vaccination against self-reported infection between 9 October 2023 and 9 January 2024 in 23,895 XBB.1.5 vaccine-eligible adults who had previously received at least one booster. VE was 41% (95% CI: 23-55) in 18-59-year-olds and 50% (95% CI: 44-56) in 60-85-year-olds. Sequencing data suggest lower protection against the BA.2.86 (including JN.1) variant from recent prior infection (OR = 2.8; 95% CI:1.2-6.5) and, not statistically significant, from XBB.1.5 vaccination (OR = 1.5; 95% CI:0.8-2.6).

Risk of COVID-19 Hospitalization and Protection Associated With mRNA Vaccination Among US Adults With Psychiatric Disorders.

Although psychiatric disorders have been associated with reduced immune responses to other vaccines, it remains unknown whether they influence COVID-19 vaccine effectiveness (VE). This study evaluated risk of COVID-19 hospitalization and estimated mRNA VE stratified by psychiatric disorder status. In a retrospective cohort analysis of the VISION Network in four US states, the rate of laboratory-confirmed COVID-19-associated hospitalization between December 2021 and August 2022 was compared across psychiatric diagnoses and by monovalent mRNA COVID-19 vaccination status using Cox proportional hazards regression. Among 2,436,999 adults, 22.1% had ≥1 psychiatric disorder. The incidence of COVID-19-associated hospitalization was higher among patients with any versus no psychiatric disorder (394 vs. 156 per 100,000 person-years, p < 0.001). Any psychiatric disorder (adjusted hazard ratio [aHR], 1.27; 95% CI, 1.18-1.37) and mood (aHR, 1.25; 95% CI, 1.15-1.36), anxiety (aHR, 1.33, 95% CI, 1.22-1.45), and psychotic (aHR, 1.41; 95% CI, 1.14-1.74) disorders were each significant independent predictors of hospitalization. Among patients with any psychiatric disorder, aHRs for the association between vaccination and hospitalization were 0.35 (95% CI, 0.25-0.49) after a recent second dose, 0.08 (95% CI, 0.06-0.11) after a recent third dose, and 0.33 (95% CI, 0.17-0.66) after a recent fourth dose, compared to unvaccinated patients. Corresponding VE estimates were 65%, 92%, and 67%, respectively, and were similar among patients with no psychiatric disorder (68%, 92%, and 79%). Psychiatric disorders were associated with increased risk of COVID-19-associated hospitalization. However, mRNA vaccination provided similar protection regardless of psychiatric disorder status, highlighting its benefit for individuals with psychiatric disorders.

Interim Effectiveness of Updated 2023-2024 (Monovalent XBB.1.5) COVID-19 Vaccines Against COVID-19-Associated Emergency Department and Urgent Care Encounters and Hospitalization Among Immunocompetent Adults Aged ≥18 Years - VISION and IVY Networks, September 2023-January 2024.

In September 2023, CDC's Advisory Committee on Immunization Practices recommended updated 2023-2024 (monovalent XBB.1.5) COVID-19 vaccination for all persons aged ≥6 months to prevent COVID-19, including severe disease. However, few estimates of updated vaccine effectiveness (VE) against medically attended illness are available. This analysis evaluated VE of an updated COVID-19 vaccine dose against COVID-19-associated emergency department (ED) or urgent care (UC) encounters and hospitalization among immunocompetent adults aged ≥18 years during September 2023-January 2024 using a test-negative, case-control design with data from two CDC VE networks. VE against COVID-19-associated ED/UC encounters was 51% (95% CI = 47%-54%) during the first 7-59 days after an updated dose and 39% (95% CI = 33%-45%) during the 60-119 days after an updated dose. VE estimates against COVID-19-associated hospitalization from two CDC VE networks were 52% (95% CI = 47%-57%) and 43% (95% CI = 27%-56%), with a median interval from updated dose of 42 and 47 days, respectively. Updated COVID-19 vaccine provided increased protection against COVID-19-associated ED/UC encounters and hospitalization among immunocompetent adults. These results support CDC recommendations for updated 2023-2024 COVID-19 vaccination. All persons aged ≥6 months should receive updated 2023-2024 COVID-19 vaccine.

Interim Influenza Vaccine Effectiveness Against Laboratory-Confirmed Influenza - California, October 2023-January 2024.

Surveillance data can provide rapid, within-season influenza vaccine effectiveness (VE) estimates to guide public health recommendations. Mandatory reporting of influenza vaccine administration to California's immunization information registry began January 1, 2023, and mandatory reporting of all influenza laboratory test results, including negative results, was instituted in California on June 15, 2023. These data, collected by the California Department of Public Health during October 1, 2023-January 31, 2024, were used to calculate interim influenza VE against laboratory-confirmed influenza by comparing the odds of vaccination among case-patients (persons who received a positive influenza laboratory test result) and control patients (those who received a negative influenza laboratory test result). VE was calculated as 1 - adjusted odds ratio using mixed-effects logistic regression, with age, race, and ethnicity as fixed effects and specimen collection week and county as random effects. Overall, during October 1, 2023-January 31, 2024, estimated VE was 45% among persons aged ≥6 months, 56% among children and adolescents aged 6 months-17 years, 48% among adults aged 18-49 years, 36% among those aged 50-64 years, and 30% among those aged ≥65 years. Consistent with some previous influenza seasons, influenza vaccination provided moderate protection against laboratory-confirmed influenza among infants, children, adolescents, and adults. All persons aged ≥6 months without a contraindication to vaccination should receive annual influenza vaccination to reduce influenza illness, severe influenza, and strain on health care resources. Influenza vaccination remains the best way to prevent influenza.

COVID-19 in City Council Civil Servants, 1 March 2020-31 January 2023: Risk of Infection, Reinfection, Vaccine Effectiveness and the Impact of Heterologous Triple Vaccination.

Background: The risk of COVID-19 increases in any occupation entailing intense social interactions. This study aimed to investigate the impact of COVID-19 among civil servants of Trieste city council (northeastern Italy) over the entire pandemic. Methods: The crude incidence rate of COVID-19 was estimated from 1 March 2020 to 31 January 2023 by explanatory factors, expressing the estimate as COVID-19 events x 10,000 person-days (P-d) at risk. A multivariable Cox proportional hazard regression model was fitted to examine the risk of primary COVID-19 infection and reinfections, reporting adjusted hazard ratios (aHR) with 95% confidence interval (95% CI). Results: The cohort of Trieste city council was mainly composed of administrative clerks (48.5%), nursery teachers (33%), technicians (9.9%) and local police officers (8.5%). Between 1 March 2020 and 31 January 2023, 1444 (62.4%) employees tested positive for SARS-CoV-2 at least once and 18.1% (=262/1444) at least twice. By the end of this study, 55% (N = 1272) of employees had received at least three doses of COVID-19 vaccine, whereas 19.7% (N = 457) remained unvaccinated. At multiple Cox regression analysis, the adjusted risk of primary COVID-19 events during the entire study period increased in employees aged 40-49 years (aHR = 1.65; 95% CI: 1.01; 2.71), females (aHR = 1.28; 95%CI: 1.12; 1.45), local police officers (aHR = 1.82; 95%CI: 1.50; 2.22) and nursery teachers (aHR = 1.27; 95%CI: 1.13; 1.43). However, whilst the risk of primary infections in police officers increased already during the Alpha transmission period (aHR = 6.82; 95%CI: 4.48; 10.40), progressively reducing across subsequent variants, for nursery teachers, it increased during the Delta wave (aHR = 2.42; 1.70; 3.44), reducing with Omicron (aHR = 1.23; 95%CI: 1.07; 1.40). Compared to unvaccinated colleagues, during the entire study period the risk of primary infections was significantly lower in employees immunized with three (aHR = 0.42; 95%CI: 0.36; 0.47) or four (aHR = 0.30; 95%CI: 0.23; 0.40) doses of COVID-19 vaccine, for a vaccine effectiveness (VE) of 58% and 70%, respectively. The protective effect of vaccination against primary infections was confirmed in the sub-group analysis by main pandemic waves, for a VE of 75% for one dose against 99% for two doses during the Alpha transmission period, slightly reducing to 59% and 70% in Delta time, respectively. During the Omicron wave, the risk of primary SARS-CoV-2 infections diminished significantly with three (aHR = 0.42; 95%CI: 0.36; 0.49) or four vaccine doses (aHR = 0.09; 95%CI: 0.05; 0.16), for a VE of 58% and 91%, respectively. Moreover, the risk of primary SARS-CoV-2 reinfections during the entire study period reduced with one (aHR = 0.47; 95%CI: 0.27; 0.82), two (aHR = 0.42; 95%CI: 0.30; 0.58), three (aHR = 0.32; 95%CI: 0.24; 0.44) or four vaccine doses (aHR = 0.14; 95%CI: 0.05; 0.46), for a VE of 53%, 58%, 68% and 86% against reinfections, respectively. No significant difference in VE was associated with heterologous versus homologous triple vaccination, both against primary infections or reinfections. Conclusions: Primary SARS-CoV-2 infections were more likely among nursery teachers and local police officers. The risk of both primary infections and reinfections reduced with higher number of doses of COVID-19 vaccine, regardless of the pandemic wave. Since city council civil servants were swab tested on demand or for contact tracing, the estimation of COVID-19 risk and VE largely missed aymptomatic SARS-CoV-2 infections. On the one hand, the present study confirmed the protective effect of COVID-19 vaccination against symptomatic SARS-CoV-2 infections; on the other hand, it highlighted not only the importance of continuous booster doses to keep up the humoral immunity over time but also the importance of updated vaccine formulations to prevent and control the spread of a highly mutable virus. Moreover, the protective effect of the first two doses against reinfections confirmed the efficacy of hybrid immunity during Omicron time.

Effectiveness of Sinopharm's BBIBP-CorV Booster Vaccination against COVID-19-Related Severe and Critical Cases and Deaths in Morocco during the Omicron Wave.

This study investigates the effectiveness of the 1st booster dose against COVID-19 severe and critical hospitalizations and deaths occurring due to the Omicron wave in Morocco. This study uses nationally representative data on COVID-19 from 15 December 2021 to 31 January 2022. The aim is to investigate the effectiveness of the inactivated COVID-19 vaccine BBIBP-CorV (Sinopharm) 1st booster dose against the Omicron wave in Morocco using real-world data established from nationally representative statistics on COVID-19 cases, deaths and vaccinations. The screening method was used to estimate vaccine effectiveness against COVID-19 severe or critical hospitalization and COVID-19-related deaths. The data were grouped by, age subgroup, sex, week, and geographical area and were analyzed using binary logistic regression with an offset for vaccine coverage. The overall BBIBP-CorV VE estimate is 89% (95% CI 85 to 92) effective in curbing COVID-19 deaths, and 81% (95% CI 78 to 84 in curbing COVID-19 severe/critical hospitalizations. Death-related VE estimate was 86% (95% CI 81 to 90) for patients aged ≥65 years, 96% (95% CI 90 to 98) for those aged <65 years, 95% (95% CI 88 to 98) in no-risk factor patients, 91% (95% CI 85 to 94) with 1 risk factor, 90% (95% CI 83 to 95) with 2 risk factors, and 72% (95% CI 52 to 84) in patients with 3 risk factors and more. Severe/critical hospitalization VE estimate was 78% (95% CI 74 to 82) for patients aged ≥65 years, 87% (95% CI 82 to 90) for those aged <65 years, 86% (95% CI 80 to 90) in no-risk factor patients, 80% (95% CI 73 to 84) with 1 risk factor, 80% (95% CI 70 to 85) with 2 risk factors, and 80% (95% CI 68 to 86) in patients with 3 risk factors and more. BBIBP-CorV boosters are effective in increasing protection against the Omicron variant-related COVID-19 deaths and severe/critical hospitalizations. The protection is reduced with older age and higher risk factors. These findings emphasize the importance of targeted vaccination strategies for different demographic groups and underscore the protective benefits of the first booster BBIBP-CorV vaccine.

Application of the screening method for estimating COVID-19 vaccine effectiveness using routine surveillance data: Germany's experience during the COVID-19 pandemic, July 2021 to March 2023.

The screening method represents a simple, quick, and practical tool for estimating vaccine effectiveness (VE) using routine disease surveillance and vaccine coverage data, even if these data cannot be linked. In Germany, where notification data, laboratory testing data, and vaccine coverage data cannot be linked due to strict data protection requirements, the screening method was used to assess COVID-19 VE continuously between July 2021 and March 2023. During this period, when Delta and Omicron variants circulated, VE estimates were produced in real-time for different age groups and clinical outcomes. Here we describe the country's overall positive experience using the screening method, including its strengths and limitations, and provide practical guidance regarding a few issues, such as case definition stringency, testing behaviour, and data stratification, that require careful consideration during data analysis and the interpretation of the results.