Highly Vaccinated Research Articles

Genomic Characterization of Three Canadian Mumps Outbreaks Demonstrates Endemic Transmission in Canada.

Despite the provision of a mumps vaccination program in Canada for over three decades, mumps has not reached elimination. Instead, a re-emergence has been observed in vaccinated populations, particularly in young adults. These outbreaks have been almost exclusively due to genotype G infections, a trend that has been seen in other countries with high mumps vaccination rates. To characterize mumps outbreaks in Canada, genomes from samples from Manitoba (n = 209), Newfoundland (n = 25), and Nova Scotia (n = 48) were sequenced and analysed by Bayesian inference. Whole genome sequencing was shown to be highly discriminatory for outbreak investigations compared to traditional Sanger sequencing. The results showed that mumps virus genotype G most likely circulated endemically in Canada and between Canada and the US. Overall, this Canadian outbreak data from different provinces and ancestral strains demonstrates the benefits of molecular genomic data to better characterize mumps outbreaks, but also suggests genomics could further our understanding of the reasons for potential immune escape of mumps genotype G and evolution in highly vaccinated populations. With a possible endemic circulation of mumps genotype G and the remaining risk of new imported cases, increased surveillance and alternative vaccination strategies may be required for Canada to reach the current target for mumps or a future elimination status.

Adapting response to a measles outbreak in a context of high vaccination and breakthrough cases: an example from Vaud, Switzerland, January to March 2024.

A measles outbreak with 51 cases occurred in the canton of Vaud, Switzerland, between January and March 2024. The outbreak was triggered by an imported case, and 37 (72.5%) subsequent cases were previously vaccinated individuals. Epidemiological investigations showed that vaccinated measles cases were symptomatic and infectious. In a highly vaccinated population, it is important to raise awareness among healthcare professionals to suspect and test for measles virus when an outbreak is declared, irrespective of the vaccination status of the patients.

Investigating the rise of Omicron variant through genomic surveillance of SARS-CoV-2 infections in a highly vaccinated university population.

Novel variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continue to emerge as the coronavirus disease 2019 (COVID-19) pandemic extends into its fourth year. Understanding SARS-CoV-2 circulation in university populations is vital for effective interventions in higher education settings and will inform public health policy during pandemics. In this study, we generated 793 whole-genome sequences collected over an entire academic year in a university population in Indiana, USA. We clearly captured the rapidity with which Delta variant was wholly replaced by Omicron variant across the West Lafayette campus over the length of two academic semesters in a community with high vaccination rates. This mirrored the emergence of Omicron throughout the state of Indiana and the USA. Further, phylogenetic analyses demonstrated that there was a more diverse set of potential geographic origins for Omicron viruses introduction into campus when compared to Delta. Lastly, statistics indicated that there was a more significant role for international and out-of-state migration in the establishment of Omicron variants at Purdue. This surveillance workflow, coupled with viral genomic sequencing and phylogeographic analyses, provided critical insights into SARS-CoV-2 transmission dynamics and variant arrival.

The Western Australian experience of COVID-19 after the borders reopened: evaluation of public health modelling predictions.

Western Australia (WA) serves as a unique global case study on the impact of coronavirus disease 2019 (COVID-19) on an isolated, prepared and highly vaccinated population. This study builds upon the study performed by House et al. through an extended data set. To examine the impact of COVID-19 at the only quaternary hospital in WA following the border opening from 3 March to 17 July 2022. A total of 257 adults were admitted with COVID-19 under either respiratory or the intensive care unit (ICU). Admission numbers, disease severity, ICU admission, prevalence of COVID-19 deterioration risk factors, length of stay and mortality. A total of 257 patients were admitted with COVID-19, under respiratory (81.7%) and ICU (18.3%). COVID-19 was the primary reason for admission for 67.7%. Ten patients died during the study, with seven deaths attributed to COVID pneumonitis. COVID-19 severity was 37.4% mild, 37.0% moderate, 18.3% severe and 7.4% critical. Risk factors for requiring ICU included incomplete immunisation status (P = 0.011), chronic kidney disease (P = 0.008) and Aboriginal and Torres Strait Islander (ATSI) ethnicity. The WA Department of Health predicted that the number of hospitalisations and ICU cases were significantly higher than the actual number of cases. The number of hospitalisations and ICU COVID-19 cases were significantly less than predicted, likely due to high population vaccination rates prior to border opening. The main risk factors for COVID-19 severity were incomplete immunisation and ATSI ethnicity.

Mumps resurgence in a highly vaccinated population: Insights gained from surveillance in Canada, 2002–2020

Although mumps vaccination has been routine in Canada for decades, mumps cases and outbreaks continue to occur periodically. Mumps surveillance, including monitoring of the mumps virus genotype associated with disease activity, is important to document baseline activity and to advance further research into vaccine effectiveness. Here we describe a detailed analysis of mumps cases that have been detected in Canada from 2002 to 2020, with a focus on the mumps molecular epidemiology. In total, 7395 cases of mumps were reported to the surveillance system, with outbreaks occurring in the years 2007, 2010 and 2016 to 2018. Adolescents and young adults aged 15 to 29 years had the highest risk of being a case (rate ratios ranging from 1.50 to 2.29), compared to adults aged 30 to 39. Genotypes of mumps viruses were determined in 3225 specimens. Genotype G was predominantly detected (96% of genotyped specimens) and was first reported in 2005. Other genotypes were more likely to be detected in cases that also reported travel (or were linked to imported cases) than the cases with genotype G detected (p < 0.0001). The genotype G viruses had little sequence diversity in the 316 nucleotide window used for genotyping (the small hydrophobic protein gene) and mainly belonged to a single phylogenetic lineage that included the MuVi/Sheffield.GBR/1.05 reference sequence. The analysis of over ten years of data has demonstrated that mumps genotype G, specifically belonging to a single lineage, the Sheffield lineage, is the endemically circulating virus in Canada. This lineage is seen also in other countries using the genotype A vaccine. Mumps remains endemic despite high MMR vaccination coverage which has been sufficient to eliminate circulation of measles and rubella in Canada, raising the hypothesis of the evolution towards a vaccine escape mumps virus.

2.M. Workshop: Empowering examples of high vaccination in minorities: learning from three underserved communities

Abstract Childhood vaccine uptake in most minority or ethnic communities in Europe is typically substantially and unacceptably lower compared to the general population. Ethnic, religious, or cultural minorities are more likely to encounter health system barriers to accessing health care services which are a major contributor to comparatively low vaccine uptake among these disadvantaged communities. Despite these challenges, some minority communities manage to achieve high uptake for childhood immunization sometimes higher than the general population in their respective countries. We have called these populations “empowering examples”. As part of RIVER-EU (Reducing Inequalities in Vaccine uptake in the European region - Engaging Underserved communities) an EU funded project aiming to improve access to vaccine services for children and youth, reducing inequality and improving vaccine uptake of HPV and MMR vaccination in underserved communities in Europe, we collected evidence on health system barriers and enablers to vaccination among underserved communities, including three empowering examples of underserved minority communities that achieve high vaccine uptake: the Somali community in Finland, the Arab community in Israel, and the Bangladeshi community in the United Kingdom. Understanding enablers to vaccination in these populations will help generate knowledge that will be translated to other populations in order to facilitate similar enablers, thus improving vaccine uptake. The main objective of this workshop is to share and discuss the preliminary findings related to health system enablers from these three “empowering examples.” The workshop will be structured in 3 presentations of 12 minutes each. Each empowering example will present preliminary findings from interviews and focus group sessions conducted with each minority community. Presentations will be followed by a moderated questions and answers session that will help the audience understand what factors have contributed high vaccine uptake in these populations and how they can be applied to others. Participants will be invited to share experiences from their own countries. Key messages • Accessibility, trust in the health care system, and perceived vaccine safety, were found to be powerful health system enablers to HPV and MMR vaccination among three underserved populations studied. • Normalizing vaccination as “just something you do” seems to be a common approach among the highly vaccinated minorities.

Vaccine effectiveness against Delta, Omicron BA.1, and BA.2 in a highly vaccinated Asian setting: a test-negative design study

ObjectivesWe compared the vaccine effectiveness over time of the primary series and booster against infection and severe disease with the Delta, Omicron BA.1, and BA.2 variants in Singapore, an Asian setting with high vaccination coverage. MethodsWe conducted a test-negative case-control study on all adult residents in Singapore who underwent PCR testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in acute hospitals. Individuals with a negative PCR from 1 September, 2021, to 30 November, 2021, and 1 December, 2021, to 25 April, 2022, served as controls for the Delta and Omicron variants respectively, and PCR-positive individuals within these two time periods served as cases. Associations between vaccination status and SARS-CoV-2 infection and severe disease with the Delta or Omicron variants were measured using Poisson regressions. Vaccine effectiveness was calculated by taking 1 minus risk ratio. ResultsThere were 68 114 individuals comprising 58 495 controls and 9619 cases for the Delta period, of whom 53 093 completed the primary series and 9161 were boosted. For the Omicron period, 104 601 individuals comprising 80 428 controls, 8643 BA.1 cases, and 15 530 BA.2 cases were included, of whom 29 183 and 71 513 were vaccinated with the primary series and boosted, respectively. The primary series provided greater protection against infection with Delta (45%, 95% CI 40–50%) than against infection with Omicron (21%, 95% CI 7–34% for BA.1; 18%, 95% CI 6–29% for BA.2) at <2 months from vaccination. Vaccine effectiveness of the booster was similar against infection with BA.1 (44%, 95% CI 38–50%) and BA.2 (40%, 95% CI 35–40%). Protection against severe disease by the booster for BA.1 (83%, 95% CI 76–88%) and BA.2 (78%, 95% CI 73–82%) was comparable to that by the primary series for Delta (80%, 95% CI 73–85%). ConclusionOur findings support the use of a booster dose to reduce the risk of severe disease and mitigate the impact on the healthcare system in an Omicron-predominant epidemic.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Outbreak at a College With High Coronavirus Disease 2019 (COVID-19) Vaccination Coverage-Connecticut, August 2021-September 2021.

BackgroundDuring August–September 2021, a Connecticut college experienced a large SARS-CoV-2 Delta outbreak despite high (99%) vaccination coverage, indoor masking policies, and twice weekly reverse transcription-polymerase chain reaction (RT-PCR) testing. The Connecticut Department of Public Health investigated characteristics associated with infection and phylogenetic relationships among cases.MethodsA case was a SARS-CoV-2 infection diagnosed by RT-PCR or antigen test during August–September 2021 in a student. College staff provided enrollment data, case information, and class rosters. An anonymous online student survey collected demographics, SARS-CoV-2 case and vaccination history, and activities the weekend before the outbreak. Multivariate logistic regression identified characteristics associated with infection. Phylogenetic analyses compared 115 student viral genome sequences with contemporaneous community genomes.ResultsOverall, 199/1788 students (11%) had lab-confirmed SARS-CoV-2 infection; most were fully vaccinated (194/199, 97%). Attack rates were highest among sophomores (72/414, 17%) and unvaccinated students (5/18, 28%). Attending in-person classes with an infectious student was not associated with infection (adjusted odds ratio [aOR] 1.0; 95%CI 0.5–2.2). Compared with uninfected students, students reporting an infection were more likely sophomores (aOR 3.3; 95%CI 1.1–10.7), attended parties/gatherings before the outbreak (aOR 2.8; 95%CI 1.3–6.4), and completed a vaccine series ≥180 days prior (aOR 5.5; 95%CI 1.8–16.2). Phylogenetic analyses suggested most cases derived from a common viral source.ConclusionsThis college SARS-CoV-2 outbreak occurred in a highly vaccinated population with prevention strategies in place. Infection was associated with unmasked off-campus parties/gatherings, not in-person classes. Students should stay up-to-date on vaccination to reduce infection.

Evolution of human papilloma virus prevalence in a highly vaccinated region in Belgium: a retrospective cohort study in Flemish women (2010-2019).

In order to lower the incidence of cervical cancer, vaccines against high-risk types of the human papilloma virus (hrHPV) were approved and brought on the market in 2007, with a partial reimbursement for Belgian citizens younger than 18 years old. Since 2010, a school-based vaccination program ensures a high vaccination coverage in young women. In this study, the impact of the Belgian vaccination program on the prevalence of HPV 16/18 is studied, together with the evolution of the prevalence of other hrHPV types and precancerous lesions. Results of HPV typing and cytology in papanicolaou-smears from women aged 20-23 years taken between 2010 and 2019 were used. An older, nonvaccinated group of women of 40-45 years old served as a control group. A significant decrease in prevalence of HPV types 16 and 18 was found in the 20-23-years-old women, whereas no decrease was found in the age group 40-45. Alongside this decrease, a significant decrease in prevalence of subtypes 6, 11 and 31 was observed, whereas type 31 is not included in the administered vaccines. Remarkably, there was no decrease in prevalence of cytological abnormalities in the study group during this study. There was even an increase in prevalence of high-risk types 53, 58 and 67. These findings emphasise the need to maintain the screening programs, even in areas with high vaccination coverage.

Increased delta variant SARS-CoV-2 infections in a highly vaccinated medical center in Japan

The Delta variant has dominated SARS-CoV-2 infections in Tokyo, Japan from June 2021 to date. We conducted a retrospective cohort study to assess BNT162b2 vaccine effectiveness during the surge in Delta among 3,911 healthcare workers (HCWs) at a medical center of Tokyo with a high vaccination rate of 84.1%. With strict infection control protocols including universal masking, only a small number of cases among vaccinated and unvaccinated HCWs were identified before June. As Delta spread in Tokyo, 16 cases among 3,289 fully vaccinated HCWs and 11 cases among 574 unvaccinated HCWs were reported in July and August (case rate in August: 4.0 vs. 19.2 per 1,000). All breakthrough cases were confirmed as Delta. While our study confirms a robust vaccine effectiveness of BNT162b2 vaccine against Delta, rising breakthrough cases suggest that continued infection control measures are warranted in higher risk environments, even when high rates of vaccination coverage are achieved.

Sex-specific effects of aging on humoral immune responses to repeated influenza vaccination in older adults

Older adults (≥65 years of age) bear a significant burden of severe disease and mortality associated with influenza, despite relatively high annual vaccination coverage and substantial pre-existing immunity to influenza. To test the hypothesis that host factors, including age and sex, play a role in determining the effect of repeated vaccination and levels of pre-existing humoral immunity to influenza, we evaluated pre- and post-vaccination strain-specific hemagglutination inhibition (HAI) titers in adults over 75 years of age who received a high-dose influenza vaccine in at least four out of six influenza seasons. Pre-vaccination titers, rather than host factors and repeated vaccination were significantly associated with post-vaccination HAI titer outcomes, and displayed an age-by-sex interaction. Pre-vaccination titers to H1N1 remained constant with age. Titers to H3N2 and influenza B viruses decreased substantially with age in males, whereas titers in females remained constant with age. Our findings highlight the importance of pre-existing immunity in this highly vaccinated older adult population and suggest that older males are particularly vulnerable to reduced pre-existing humoral immunity to influenza.

New decade, new response: Altering the public health response to toxigenic cutaneous diphtheria

Abstract Background Classical diphtheria is a potentially fatal respiratory disease mediated by the diphtheria toxin of Corynebacterium diphtheriae. Due to high vaccination rates against this toxin in Canada, the national incidence of respiratory diphtheria is near zero, and the toxin plays no recognized role in cutaneous diphtheria. Therefore, in this study, we assessed the diagnostic and public health benefits of diphtheria toxin testing and cutaneous diphtheria investigations in a highly vaccinated population. Methods Over the last 10 years, we retrospectively determined: the number of C. diphtheriae isolates identified in the province of Alberta, Canada; the disease state of each individual tested (disease vs asymptomatic carrier); the source (cutaneous vs respiratory); and the number of toxin tests performed. Results In 10 years, zero cases of respiratory diphtheria and three cases of toxigenic cutaneous diphtheria were identified. Despite zero cases of respiratory disease, diphtheria toxin testing significantly increased (p = 0.0001), with 86% of toxin tests performed on cutaneous isolates. Subsequent public health investigations of each case of toxigenic cutaneous diphtheria mandated the collection of 315 total specimens from 92 individuals, revealing low rates of C. diphtheriae colonization among contacts and no further cases. Conclusions This study challenges the value of reflexive diphtheria toxin testing in uncomplicated cutaneous diphtheria among highly vaccinated populations. Cutaneous diphtheria investigations demanded disproportionate public health and laboratory resources and demonstrated a discrepancy between toxin pathophysiology and disease. Therefore, we recommend stewarding diphtheria toxin tests for toxin-mediated disease forms and ensuring adequate vaccination. This approach would spare public health and laboratory resources by customizing responses around the role of the diphtheria toxin in each form of disease. Key messages Investigations for cutaneous diphtheria increased demand for toxin testing in Alberta, Canada, though the toxin plays no role in this form of disease. In populations with high vaccination rates against diphtheria toxoid, cutaneous diphtheria cases do not require additional laboratory testing for the presence of the diphtheria toxin.

Measles immunity gaps in an era of high vaccination coverage: A serology study from Taiwan

BackgroundRoutine vaccination for children drastically reduces measles cases. Nonetheless, the global resurgence of measles since 2018 highlights the need for evaluating vaccine-induced immunity in an era of high vaccination coverage, especially in international travelers. This study aims to identify high-risk persons via analyzing the impact of age and different vaccination schedules on seroprevalence of measles in a country with high vaccination coverage, attempting to provide suggestions regarding pre-travel measles vaccination in highly immunized countries. MethodWe retrospectively collected serological results of measles from Taiwanese travelers during 2008–2017 and middle-aged subjects from community during 2007–2009. Participants were classified by age groups and cohort based on the national immunization program: cohort I (pre-mass vaccination), cohort II (suboptimal measles vaccination), and cohort III (2-dose MMR in childhood). The effects of age group on seropositivity was shown by odds ratio (OR) with 95% confidence interval (CI) in a logistic regression model. ResultsThe overall measles seroprevalence was 74.5% (N = 1096, mean age = 31.7 ± 12.3 years), with adolescents having the lowest seropositivity (65.9%) and participants ≥50 years having the highest (89.4%). Seropositivity was significantly higher in cohort I (pre-mass vaccination) compared with the other 2 cohorts (P < 0.0001). The effect of aging on seropositivity was only significant in cohort II (OR = 1.84, 95% CI = 1.13–2.99, P = 0.014 for 30–39 years vs. 20–29 years). ConclusionsWaning immunity to measles in adolescents and young adults is a dominant issue in highly vaccinated cohorts. Enhancing pre-travel vaccination against measles can effectively fill the immunity gaps in highly immunized countries.

Mumps: Outbreak in correctly vaccinated population of young people

IntroductionAs a consequence of the introduction of the MMR vaccine in 1980, an important decline of mumps cases and outbreaks occured. But at the beginning of the 21st century, an increase in outbreaks affecting well vaccinated youngsters harshly questions the effectiveness of the vaccine. This work describes an outbreak occuring in a highly vaccinated youngster population and the difficulties for its control. MethodsDescriptive observational study of mumps’ cases reported during the period between the 24th of August 2015 and the 12th of May 2016 in Osona county in the central Region of Catalonia. ResultsThe total number of cases reported was 162 with a median of age of 21 yrs (rank 6–56 years). A positive correlation between the number of cases and the period from the administration the last MMR vaccine and disease onset was described. Additional prevention and control are measures were recomended to control the outbreak. ConclusionsThe results highlight the need to continue immunisation programmes along with epidemiological surveillance of the disease in order to maintain high vaccine coverage and the implementation of immediate prevention and control measures. More studies are necessary to monitor the effectiveness of a third dose to improve the control of outbreaks.

Parotiditis: brote en población de jóvenes correctamente vacunada

IntroductionAs a consequence of the introduction of the MMR vaccine in 1980, an important decline of mumps cases and outbreaks occured. But at the beginning of the 21st century, an increase in outbreaks affecting well vaccinated youngsters harshly questions the effectiveness of the vaccine. This work describes an outbreak occuring in a highly vaccinated youngster population and the difficulties for its control. MethodsDescriptive observational study of mumps’ cases reported during the period between the 24th of August 2015 and the 12th of May 2016 in Osona county in the central Region of Catalonia. ResultsThe total number of cases reported was 162 with a median of age of 21 yrs (rank 6-56 years). A positive correlation between the number of cases and the period from the administration the last MMR vaccine and disease onset was described. Additional prevention and control are measures were recomended to control the outbreak. ConclusionsThe results highlight the need to continue immunization programmes along with epidemiological surveillance of the disease in order to maintain high vaccine coverage and the implementation of immediate prevention and control measures. More studies are necessary to monitor the effectiveness of a third dose to improve the control of outbreaks.

A protracted mumps outbreak in Western Australia despite high vaccine coverage: a population-based surveillance study

In 2007-08, a genotype J mumps outbreak occurred among Aboriginal people in northern Western Australia, despite high vaccine coverage. In March, 2015, a second protracted mumps outbreak occurred in northern Western Australia and spread widely across rural areas of the state. This time the outbreak was caused by a genotype G virus and again primarily affected Aboriginal people. We aimed to describe the epidemiology of this outbreak. In this population-based surveillance study, we analysed statutory notifications and public health case follow-up data from the Western Australia Notifiable Infectious Diseases Database and vaccination information from the Australian Childhood Immunisation Register. An outbreak case of mumps was notified if the affected person was living in or visiting a community in Western Australia where there was active mumps transmission, and if mumps infection was confirmed by laboratory diagnosis or by an epidemiological link. We analysed case demographics, vaccination status, and age-standardised attack rates in Aboriginal and non-Aboriginal people by region of notification. Laboratory diagnoses were made by real-time RT-PCR, serology, or both, and carried out by the sole public pathology provider in Western Australia. Between March 1, 2015, and December 31, 2016, 893 outbreak cases were notified. 798 (89%) of 893 outbreak cases were reported in Aboriginal people. 40 (4%) of 893 people were admitted to hospital, and 33 (7%) of 462 men reported orchitis. Mumps attack rates increased sharply with age, peaking in the 15-19 age group. 371 (89%) of 419 people aged 1-19 years were fully vaccinated and 29 (7%) were partly vaccinated. Of the 240 people who tested positive by real-time RT-PCR and had also been tested for mumps-specific IgG and IgM, 165 (69%) were positive for IgG but negative for IgM, indicating the importance of RT-PCR testing for diagnosis in vaccinated populations. None of the cases from the 2007-08 genotype J outbreak were re-notified. The number of mumps outbreaks reported in recent years among highly vaccinated populations, including Indigenous populations, has been growing. More widespread and pre-emptive use of the third dose of measles, mumps, and rubella vaccine might be required to control and prevent future outbreaks in high-risk populations. Research should explore the benefit of increasing the intervals between vaccine doses to strengthen the durability of vaccine protection. None.

Measles Outbreak in a Highly Vaccinated Population - Israel, July-August 2017.

On August 6, 2017, the Israeli Defense Force Public Heath Branch (IDFPHB) was notified of two suspected measles cases. IDFPHB conducted an epidemiologic investigation, which identified nine measles cases in a population with high measles vaccination coverage. All measles patients had signs and symptoms consistent with modified measles (i.e., less severe disease with milder rash, fever, or both, with or without other mild typical measles symptoms). A total of 1,392 contacts were identified, and 162 received postexposure prophylaxis (PEP) with measles-mumps-rubella (MMR) vaccine; the remaining contacts were followed for 21 days (one incubation period). No tertiary cases were identified.

Humoral immunity to mumps in a highly vaccinated population in Taiwan.

A resurgence of mumps was noted recently and outbreaks were increasingly reported in populations with high vaccine coverage. We aimed to evaluate the seroprevalence to mumps in Taiwan, where a two-dose childhood mumps-containing vaccine program, with a high coverage rate, had been implemented for >20 years. The anti-mumps IgG was determined in 3552 participants of all ages in Taiwan. The age-specific seropositivity rates were calculated and the sociodemographic variables associated with the seronegative sera were analyzed with a logistic regression method. The overall seroprevalence to mumps was 71%, with a higher rate in adults ≥19 years old than in the pediatric population <19 years old (80.4% versus 62.0%, P<0.0001). In participants aged 2-20 years, who had been given at least one mumps-containing vaccine, the seropositivity fluctuated across different age subgroups and the lowest rate (36.8%) occurred in the 17-18 years age group. The multivariate analysis identified age within 17-18 years (adjusted odds ratio [aOR] 8.598, 95% confidence interval [CI] 2.990-24.722, P<0.0001), within 19-20 years (aOR 5.076, 95% CI 1.702-15.133, P=0.0080), and being a resident of the suburban area of northern Taiwan (aOR 1.089, 95% CI 0.823-1.414, P=0.0008) as independent factors associated with an increased risk of seronegative sera. The seropositivity to mumps was unexpectedly low in highly vaccinated generations, and with a significant geographical discrepancy in Taiwan, which may have been responsible for the sustained reports of mumps cases in Taiwan.

Varicella outbreak in a highly-vaccinated school population in Beijing, China during the voluntary two-dose era.

Two-dose varicella vaccination has been available in Beijing since 2012 in the private sector. We investigated a varicella outbreak in a highly vaccinated elementary school population. A cohort study was carried out and a varicella case was defined as an acute onset of generalized maculopapulovesicular rash without other apparent cause in a student attending the school from March 29 through May 17, 2015. Breakthrough varicella was defined as varicella >42days after the last vaccine dose among both 1- or 2-dose varicella vaccine recipients. Vaccination information was collected from immunization records; information on prior varicella and clinical presentations was collected by surveying students' parents. Of the 1056 students in the school, 1027 (97.3%) reported no history of varicella. Prior to the outbreak, 98.6% of students had received ≥1 dose of varicella vaccine, and most (63.2%) students received two doses. Twenty varicella cases were identified for an overall attack rate of 2.0%. Half of the cases occurred in the classroom of the index case-patient, a two-dose recipient who was not isolated after symptom onset. Breakthrough varicella accounted for 95% of cases (19/20) with attack rates of 14.3% (1/7), 1.6% (6/362) and 2.0% (13/649) among unvaccinated, one-dose, and two-dose students, respectively. Most case-patients (18/20, 90%) had <50 lesions. No difference in clinical presentations was found between one-dose and two-dose recipients with breakthrough varicella. Moderate two-dose varicella vaccine coverage was insufficient to prevent a varicella outbreak. Two-dose recipients with breakthrough varicella are contagious. High two-dose varicella vaccine coverage and timely isolation of cases may be needed for varicella outbreak prevention in the two-dose era.

Influenza vaccination responses: Evaluating impact of repeat vaccination among health care workers

ObjectiveTo compare the antibody response to influenza between health care workers (HCWs) who have received multiple vaccinations (high vaccination group) and those who have received fewer vaccinations (low vaccination group). DesignProspective serosurvey. SettingTertiary referral hospital. ParticipantsHealthcare workers. MethodsHealthcare workers were vaccinated with the 2015 southern hemisphere trivalent influenza vaccine. Influenza antibody titres were measured pre-vaccination, 21–28days post-vaccination and 6months post-vaccination. Antibody titres were measured using the haemagglutination inhibition assay. Levels of seropositivity and estimated geometric mean titres were calculated. ResultsOf the 202 HCWs enrolled, 182 completed the study (143 high vaccination and 39 low vaccination). Both vaccination groups demonstrated increases in post-vaccination geometric mean titres, with greater gains in the low vaccination group. Seropositivity remained high in both high and low vaccination groups post-vaccination. The highest fold rise was observed among HCWs in the low vaccination group against the H3N2 component of the vaccine. ConclusionsBoth high and low vaccination groups in our study demonstrated protective antibody titres post-vaccination. The findings from the current study are suggestive of decreased serological response among highly vaccinated HCWs. More studies with larger sample sizes and a greater number of people in the vaccine-naïve and once-vaccinated groups are required to confirm or refute these findings before making any policy changes.