Estimating age-specific vaccine effectiveness using data from a large measles outbreak in Berlin, Germany, 2014/15: evidence for waning immunity

A Nationwide Seroprevalence Study for Measles in Individuals of Fertile Age in Romania

Background/Objectives: Romania remains endemic for measles due to suboptimal vaccine coverage rates. During the last three epidemics, the highest incidence of measles was recorded in children younger than 1 year, who should have been partially protected by maternal antibodies. A nationwide cross-sectional seroprevalence study was conducted on persons of fertile age, to evaluate potential immunity gaps in the population. Methods: Between June and October 2020, 959 serum samples were collected from individuals aged 25-44 years (46.5% females) from all the geographic regions in Romania. Measles IgG antibodies were assessed using an enzyme-linked immune assay (DIA.PRO-Diagnostic Bioprobes Srl, Italy). Statistical analysis was performed in IBM SPSS Statistics 27.0, using Fisher's exact and chi-squared tests to test for associations between seropositivity and demographic factors, with p < 0.05 considered statistically significant. Results: The overall measles seroprevalence was 77%, without gender- or geographic region-related differences. Both the seropositivity rate and the measles antibodies titers increased with age, with the highest difference between the oldest and the youngest age group (p = 0.057), suggesting persistent immunity after natural infection in older individuals or anamnestic responses in vaccinated persons, caused by repeated exposures to the circulating virus. An additional confirmatory pilot study on 444 pregnant women confirmed the low level of measles seroprevalence (68.4%), with a significant upward trend in older ages (75% in those aged >40 years old vs. 65% in those aged 25-29 years, p = 0.018 and mean reactivity of measles antibodies 3.05 ± 1.75 in those aged >40 years vs. 2.28 ± 1.39 in those aged 25-29 years, p = 0.037). Conclusions: This study signals critical immunity gaps in the population that contribute to the accumulation of susceptible individuals and recurrent measles outbreaks. The absence of measles antibodies in women of childbearing age increases the newborn's susceptibility to infection, with potentially severe complications.

Estimating waning immunity against classical swine fever virus among adult wild boar: A case study in Japan

Bait vaccination against classical swine fever virus (CSFV) among wild boar in Japan started in 2019 and has continued so far. While the proportion of immune individuals increased in the early phase of the CSFV epidemic, this proportion tended to decrease in some regions, even after the subsequent vaccination. Turnover of wild boar populations can reduce the proportion of immune individuals; however, the decrease was also observed among adult wild boar during the season when the influence of turnover was negligible. Waning immunity is hypothesized as an alternative mechanism. This study aimed to test the hypothesis of waning immunity and estimate the waning rate among wild boar. A mathematical model describing CSFV transmission dynamics, host population dynamics, effect of vaccination, and waning immunity was constructed. We also constructed a model without waning immunity. The two models were fitted to a time-series of the proportion of recovered/vaccinated animals (i.e., ELISA-positive and PCR-negative) among adult wild boar in Gifu, Japan, assuming that the influence of turnover was negligible from July to November. The hypothesis that immunity against CSFV can wane is accepted; the model with waning immunity showed a significantly better fit compared to another model. The time until ELISA test results became negative after recovery/vaccination was estimated to be 26.6 weeks. Our results imply that the acquired immunity against CSFV and bait vaccination wanes over time. The level of herd immunity after vaccination against CSFV should be evaluated taking the waning immunity into account.

Measles vaccine effectiveness in African children: a systematic review and meta-analysis

INTRODUCTION

Measles is an extremely contagious viral disease that can be prevented through vaccination. It is caused by the measles virus and presents with symptoms such as high fever, cough, runny nose, conjunctivitis, and a distinctive rash. Complications may include pneumonia, diarrhoea, and neurological issues. The disease spreads through respiratory droplets and continues to pose a significant public health challenge, especially in Africa, despite vaccination efforts.

OBJECTIVE

This systematic review and meta-analysis aim to estimate the pooled vaccine effectiveness of measles vaccines among African children, providing insights into immunization program success and informing policy decisions on vaccine distribution and resource allocation.

METHODS

Following PRISMA guidelines, search was conducted in databases including PubMed/Medline, Science Direct, HINARI, Cochrane/Wiley library, Europe PMC, and grey literatures like Google Scholar up to March 2024. Cross-sectional studies assessed measles vaccine effectiveness in African children aged nine months and above were included. Data was extracted using JBI extraction tool and entered into microsoft excel and analysed via STATA version 20.1 using random effect model.

RESULTS

From 5295 identified articles, 18 met the inclusion criteria, encompassing 26,470 children from 13 African countries. The pooled measles vaccine effectiveness was 68.58%, with significant heterogeneity (I2 = 99.66%, p < 0.001). Subgroup analysis showed variability in vaccine effectiveness by study period, with higher effectiveness in studies conducted after the Global Vaccine Action Plan (GVAP) in 2012.

CONCLUSION

Measles vaccine effectiveness varies in African regions, ranging from 98.4% in Nigeria to 36.5% in Mozambique, with an overall effectiveness of 68.58% and high heterogeneity among studies. Optimizing vaccine distribution, increasing coverage, and prompt administration are important for enhancing effectiveness. Continued support for GVAP strategies and further research is needed to understand factors affecting vaccine performance and improve immunization efforts in Africa.

Long-term waning of vaccine-induced immunity to measles in England: a mathematical modelling study

BACKGROUND

Among people infected with measles in England between 2010 and 2019, the proportion of cases who had previously received two doses of vaccine has increased, especially among young adults. Possible explanations include rare infections in vaccinated individuals who did not gain immunity upon vaccination, made more common because fewer individuals in the population were born in the endemic era, before vaccination was introduced, and exposed as part of endemic transmission, or the waning of vaccine-induced immunity, which would present new challenges for measles control in near-elimination settings. We aimed to evaluate whether measles dynamics observed in England between 2010 and 2019 were in line with a waning of vaccine-induced immunity.

METHODS

We used a compartmental mathematical model stratified by age group, region, and vaccine status, fitted to individual-level case data reported in England from 2010 to 2019 and collected by the UK Health Security Agency. The deterministic model was fitted using Monte Carlo Markov Chains under three scenarios: without the waning of vaccine-induced immunity, with waning depending on time since vaccination, and with waning depending on time since vaccination, starting in 2000. We generated stochastic simulations from the fitted parameter sets to evaluate which scenarios could replicate the transmission dynamics observed in vaccinated cases in England.

FINDINGS

The scenario without waning overestimated the number of one-dose recipients among measles cases, and underestimated the number of two-dose recipients among cases older than 15 years (median 75 cases [95% simulation interval (SI) 44-124] in simulations without waning, 196 [95% SI 122-315] in simulations when waning was included, 188 [95% SI 118-301] in simulations when waning started in 2000, and 202 observed cases). The number of onward transmissions from vaccinated cases was 83% (95% credible interval 72-91%) of the number of transmissions from unvaccinated cases. The estimated waning rate was slow (0·039% per year of age; 95% credible interval 0·034-0·044% per year in the best-fitting scenario with waning starting in 2000), but sufficient to increase measles burden.

INTERPRETATION

Measles case dynamics in England are consistent with scenarios assuming the waning of vaccine-induced immunity. Since measles is highly infectious, slow waning leads to a heightened burden in outbreaks, increasing the number of measles cases in people who are both vaccinated and unvaccinated. Our findings show that although the vaccine remains highly protective against measles infections for decades and most transmission is connected to people who are unvaccinated, breakthrough infections are increasingly frequent for individuals aged 15 years and older who have been vaccinated twice.

FUNDING

National Institute for Health and Care Research and Wellcome Trust.

Two-dose measles vaccine effectiveness remains high over time: A French observational study, 2017-2019

BACKGROUND

From 2008 to 2019, France has experienced a resurgence of measles epidemics. Surveillance data have shown that the proportion of cases vaccinated with two doses of measles-containing vaccine (MCV) increased with age, raising concerns about the duration of vaccine protection. Our objectives were to investigate age-stratified vaccine effectiveness (VE) for the second dose of MCV (MCV2) and to quantify protection levels over time.

METHODS

We analyzed data on measles cases aged 2-31 years, reported via mandatory notification to the French measles surveillance system from October 2017 to September 2019. We estimated an age-stratified VE for MCV2 using the screening method, which compares the vaccination status of cases with that of the general population. We improved this method by accounting for natural immunity, exploring four scenarios with four possible levels of natural immunity in the population. In addition, we quantified the decay rate of protection over time, by fitting an exponential decay model among individuals vaccinated in early life.

RESULTS

In the baseline analysis (absence of natural immunity), VE estimates were high in all age groups and decreased with age, from 99.6 % (95 % confidence interval: 99.3-99.8) in 2-5 years old to 91.4 % (85.1-95.0) in 26-31 years old. Accounting for natural immunity increased VE in the older age group to 93.2-99.2 % depending on the scenario. We estimated that VE was slowly decreasing over time, with an exponential decay rate of 0.0022/year (0.0017-0.0028), leading to VE of 96.7 % (96.0-97.4) 16 years after MCV2 vaccination. This decline was most compatible with scenario 2, a scenario of 4.4 % naturally immunized, non-vaccinated individuals in the 26-31 years old.

CONCLUSION

Our study confirms the continued high effectiveness of two doses of MCV with only slight degradation, decades after immunization. These findings support the importance of achieving a very high vaccination coverage with 2 doses of MCV.

Effect of vaccine program on IgG antibody titers for measles, rubella, varicella, and mumps in young adults in Japan: Survey between 2018 and 2021

INTRODUCTION

Improved routine immunizations in Japan have led to a reduction in vaccine-preventable diseases. Due to changes in the vaccination program, current young adults received their second vaccination for measles and rubella at different times depending on their birth year, and most of them have not been vaccinated against varicella and mumps. This study investigated the effect of vaccine programs on the immunity of people in Japan.

METHODS

Immunoglobulin G antibody (IgG) titers against four viruses were determined by enzyme immunoassay in 795 students at a medical university. Titers for measles and rubella were compared according to the students' birth dates (Group 1: April 2, 1990-April 1, 2000; Group 2: April 2, 2000).

RESULTS

The titers of students that satisfied the standard IgG values against measles, rubella, varicella, and mumps were 24.3%, 56.9%, 87.4%, and 47.2%, respectively. Measles and rubella titers were lower in group 2 (estimated mean period from last vaccination, 7.0 years) than group 1 (13.5 years) (p = 0.023 measles, p = 0.037 rubella), indicating attenuation of titers over time. Varicella and mumps antibody prevalence indicated that these infections were endemic, whereas rates of negative titers were higher than those for measles and rubella.

CONCLUSIONS

IgG titers against viruses were affected by vaccination programs. Declining titers after vaccination should be monitored when the diseases are almost eliminated and boosting is absent. Antibody testing is meaningful for recommending vaccinations and for surveillance of waning immunity. Continuous improvements of vaccination program should be considered to prevent and eliminate diseases.

Evolving measles status and immunization policy development in six European countries

Developing and implementing new immunization policies in response to shifting epidemiology is a critical public health component. We adopted a mixed-methods approach (via narrative literature review [101 articles] and 9 semi-structured interviews) to evaluate policy development in response to shifting measles epidemiology in six European countries (Italy, Belgium, Germany, Romania, UK, and Ukraine); where policies and strategies have evolved in response to country-specific disease and vaccination patterns. Periodic outbreaks have occurred in all countries against a background of declining measles-containing-vaccine (MCV) uptake and increasing public vaccine hesitancy (with substantial regional or social differences in measles burden and vaccine uptake). Health-care worker (HCW) vaccine skepticism is also seen. While many outbreaks arise or involve specific susceptible populations (e.g., minority/migrant communities), the broader pattern is spread to the wider (and generally older) population; often among incompletely/non-vaccinated individuals as a legacy of previous low uptake. Immunization policy and strategic responses are influenced by political and social factors, where public mistrust contributes to vaccine hesitancy. A strong centralized immunization framework (allied with effective regional implementation and coherent political commitment) can effectively increase uptake. Mandatory vaccination has increased childhood MCV uptake in Italy, and similar benefits could be anticipated for other countries considering vaccine mandates. Although possible elsewhere, socio-political considerations render mandating impractical in other countries, where targeted immunization activities to bolster routine uptake are more important. Addressing HCW skepticism, knowledge gaps, improving access and increasing public/community engagement and education to address vaccine hesitancy/mistrust (especially in communities with specific unmet needs) is critical.

Specifically Increased Rate of Infections in Children Post Measles in a High Resource Setting

OBJECTIVES

Post-measles increased susceptibility to subsequent infections seems particularly relevant in low-resource settings. We tested the hypothesis that measles causes a specifically increased rate of infections in children, also in a high-resource setting.

METHODS

We conducted a retrospective cohort study on a large measles outbreak in Berlin, Germany. All children with measles who presented to hospitals in Berlin were included as cases, children with non-infectious and children with non-measles infectious diseases as controls. Repeat visits within 3 years after the outbreak were recorded.

RESULTS

We included 250 cases, 502 non-infectious, and 498 infectious disease controls. The relative risk for cases for the diagnosis of an infectious disease upon a repeat visit was 1.6 (95% CI 1.4-2.0, p < 0.001) vs. non-infectious and 1.3 (95% CI 1.1-1.6, p = 0.002) vs. infectious disease controls. 33 cases (27%), 35 non-infectious (12%) and 57 (18%) infectious disease controls presented more than three times due to an infectious disease (p = 0.01, and p = 0.02, respectively). This results in a relative risk of more than three repeat visits due to an infection for measles cases of 1.8 (95% CI 1.3-2.4, p = 0.01), and 1.4 (95% CI 1.0-1.9, p = 0.04), respectively.

CONCLUSION

Our study demonstrates for the first time in a high-resource setting, that increased post-measles susceptibility to subsequent infections in children is measles-specific-even compared to controls with previous non-measles infections.

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.

The Role of Sex, Ethnicity, Age, and Nutritional Status in the Seropositivity of the Measles Vaccine

AIM: This study investigates the relationship between sex, ethnicity, age, nutritional status with the seropositivity of the Edmonston-Zagreb vaccine in children. METHODS: A cross sectional, observational study was conducted. A total of 45 children were differentiated based on sex, ethnicity, age, and nutritional status when they received the Edmonston-Zagreb measle vaccine for the first time. Flow cytometry was used to look at differences in antibody status as well as populations of CD-4 and CD-8 cells that release IFN- γ. RESULTS: We found no significant differences in antibody levels or CD-4 and CD-8 cell populations that secrete IFN- γ between boys and girls (p > 0.05). Besides, similar results were also confirmed in comparisons between Javanese and Sundanese ethnic groups, 9 months versus more than 9 months of age, or normal versus low body mass index (p > 0.05). CONCLUSIONS: We conclude that sex, race, age, and nutritional status had no effect on immune response to vaccination. As a result, there was no barrier to seroconversion and optimal immunological performance in the children in this trial who received the Edmonston-Zagreb measles vaccination.

Measles, mumps, rubella prevention: how can we do better?

INTRODUCTION

Measles, mumps, and rubella incidence decreased drastically following vaccination programs' implementation. However, measles and mumps' resurgence was recently reported, outbreaks still occur, and challenges remain to control these diseases.

AREAS COVERED

This qualitative narrative review provides an objective appraisal of the literature regarding current challenges in controlling measles, mumps, rubella infections, and interventions to address them.

EXPERT OPINION

While vaccines against measles, mumps, and rubella (including trivalent vaccines) are widely used and effective, challenges to control these diseases are mainly related to insufficient immunization coverage and changing vaccination needs owing to new global environment (e.g. traveling, migration, population density). By understanding disease transmission peculiarities by setting, initiatives are needed to optimize vaccination policies and increase vaccination coverage, which was further negatively impacted by COVID-19 pandemic. Also, awareness of the potential severity of infections and the role of vaccines should increase. Reminder systems, vaccination of disadvantaged, high-risk and difficult-to-reach populations, accessibility of vaccination, healthcare infrastructure, and vaccination services management should improve. Outbreak preparedness should be strengthened, including implementation of high-quality surveillance systems to monitor epidemiology. While the main focus should be on these public health initiatives to increase vaccination coverage, slightly more benefits could come from evolution of current vaccines.

Ten years of weekly epidemiological teleconference (EpiLag) - an effective and time-efficient tool for infectious disease event information, Germany, 2009-2018

In 2009, the Robert Koch Institute (RKI) and the 16 German federal state public health authorities (PHAs) established a weekly epidemiological teleconference (EpiLag) to discuss infectious disease (ID) events and foster horizontal and vertical information exchange. We present the procedure, discussed ID topics and evaluation results of EpiLag after 10 years. We analysed attendance, duration of EpiLag and the frequency of reported events. Participants (RKI and state PHA) were surveyed regarding their satisfaction with logistics, contents and usefulness of EpiLag (Likert scales). Between 2009 and 2018, RKI hosted 484 EpiLag conferences with a mean duration of 25 min (range: 4–60) and high participation (range: 9–16; mean: 15 PHAs). Overall, 2975 ID events (39% international, 9% national and 52% subnational) were presented (mean: 6.1 per EpiLag), most frequently on measles (18%), salmonellosis (8%) and influenza (5%). All responding participants (14/16 PHAs and 9/9 at RKI) were satisfied with the EpiLag's organization and minutes and deemed EpiLag useful for an overview and information distribution on ID events relevant to Germany. EpiLag is time efficient, easily applicable and useful for a low-threshold event communication. It supports PHAs in crises and strengthens the network of surveillance stakeholders. We recommend its implementation to other countries or sectors.

Durability of humoral immune responses to rubella following MMR vaccination

BACKGROUND

While administration of the measles-mumps-rubella (MMR-II®) vaccine has been effective at preventing rubella infection in the United States, the durability of humoral immunity to the rubella component of MMR vaccine has not been widely studied among older adolescents and adults.

METHODS

In this longitudinal study, we sought to assess the durability of rubella virus (RV)-specific humoral immunity in a healthy population (n = 98) of adolescents and young adults at two timepoints: ~7 and ~17 years after two doses of MMR-II® vaccination. Levels of circulating antibodies specific to RV were measured by ELISA and an immune-colorimetric neutralization assay. RV-specific memory B cell responses were also measured by ELISpot.

RESULTS

Rubella-specific IgG antibody titers, neutralizing antibody titers, and memory B cell responses declined with increasing time since vaccination; however, these decreases were relatively moderate. Memory B cell responses exhibited a greater decline in men compared to women.

CONCLUSIONS

Collectively, rubella-specific humoral immunity declines following vaccination, although subjects' antibody titers remain well above the currently recognized threshold for protective immunity. Clinical correlates of protection based on neutralizing antibody titer and memory B cell ELISpot response should be defined.

Surprisingly Low Levels of Measles Immunity in Persons With HIV: A Seroprevalence Survey in a United States HIV Clinic

Background

Measles outbreaks have become increasingly common due to deteriorating vaccination rates, fluctuating herd immunity, and varying antibody decline. Limited knowledge exists regarding prevalence and risk factors associated with measles seronegativity among persons with HIV (PWH).

Methods

This was a cross-sectional study conducted at an academic HIV clinic in Omaha, Nebraska. Participants were screened for the presence of measles IgG antibody. Demographic and clinical information was obtained through electronic medical record review. Simple and multivariable logistic regressions were performed to identify risk factors for measles seronegativity.

Results

Three hundred fifty-one participants were enrolled, with a measles seroprevalence rate of 70.3%. The mean age (range) was 48 (20-74) years, 77% were male, and 53% were Caucasian. The mean CD4 nadir (range) was 334 (1-1675) cells/mm³. At the time of testing, 86% and 87% of the seronegative and seropositive participants had an HIV RNA <50 copies/mL, respectively. Younger age was significantly associated with measles seronegativity (P = .003), as was birth year after 1957 (P = .021). Prior history of measles infection was associated with seropositivity (P = .011). All other risk factors evaluated, including written documentation of adequate vaccination, were not associated with seronegativity.

Conclusions

Our study demonstrates a measles seroprevalence rate that is remarkably lower than previously reported in PWH (92%), and, more importantly, is considerably lower than the rate needed to maintain herd immunity (95%). With higher than expected seronegativity and absence of notable risk factors aside from age, our findings support expanded measles immunity screening for PWH who are at risk of measles exposure.

Vaccine-Preventable Infections in Childcare Workers

BACKGROUND

Adequate immunity to so-called childhood diseases can lower the occupational risk of vaccine-preventable infectious diseases in persons who work in day-care centers for children.

METHODS

A systematic literature survey was carried out in PubMed and Embase for the period January 2000 to February 2019. Studies on immune status and vaccination status were included. In addition, data from the first wave of the German Health Interview and Examination Survey for Adults (Studie zur Gesundheit Erwachsener in Deutschland, DEGS1) and surveillance data on notifiable infections in Germany were evaluated.

RESULTS

Six studies and the DEGS1 analysis of vaccination or immune status for varicella zoster, rubella, hepatitis A (HAV), pertussis, measles, and mumps in persons caring for children in day-care centers, most of whom are women, were included in this review. According to DEGS1, childcare workers are more commonly vaccinated against HAV and pertussis than the general female population (prevalence ratios [PR]: 1.46 [1.12; 1.90] and 1.57 [1.05; 2.36]), yet 57% had not been vaccinated against HAV and 77% had not been vaccinated against pertussis. Childcare workers were found to be less commonly vaccinated against rubella than the general female population, although the difference was not statistically significant (PR: 0.87 [0.71; 1.07]). In a Canadian study, positive HAV serology was found to be correlated with the duration of activity as a childcare worker. In the DEGS1 study, large proportions of the younger childcare workers in particular were seronegative against measles (16%), mumps (19%), and HAV (37%). Notifiable disease statistics show that those working in community facilities had a markedly higher risk of mumps, pertussis, and varicella (relative risk [RR]: 1.8-2.6) and a somewhat higher risk of rubella and HAV (RR: 1.47 and 1.21, respectively).

CONCLUSION

Childcare workers have a higher occupational risk of infection but do not always receive the appropriate vaccinations. In particular, women of child-bearing age working in day-care centers should be made more aware of the need for vaccination.

Investigation and control of a measles outbreak at the Hong Kong Special Administrative Region International Airport, 2019

INTRODUCTION

Hong Kong Special Administrative Region SAR (China) achieved measles elimination status in 2016, and the incidence of measles infection had been low over the past few years. However, the Centre for Health Protection (CHP) at the Department of Health was notified on 22 March 2019 of an outbreak of three cases of measles infection among workers at the Hong Kong Special Administrative Region International Airport (HKIA).

METHODS

We reviewed notifications of measles received by CHP from 1 January to 17 May 2019. We defined a confirmed case of measles as having laboratory evidence of measles infection. All confirmed cases among airport workers or those with epidemiological information suggesting they had been infected by contact with airport workers were included in the review. We described the epidemiological features and reviewed the control measures against the outbreak.

RESULTS

We identified 33 cases, 29 of which were among airport workers. They comprised 22 men and 11 women, aged 20-49 years (median 25 years). The majority of people with confirmed measles presented with fever and rash. All required hospitalization. None developed complications. Control measures, including enhanced environmental hygiene and improved ventilation at HKIA and vaccinations for the airport community, were implemented. Vaccinations were provided to 8501 eligible airport workers, and the outbreak was declared over on 17 May 2019.

DISCUSSION

Early recognition of the outbreak and prompt control measures, especially targeted vaccination of the exposed population, effectively controlled the outbreak in just two weeks.

The effect of time since measles vaccination and age at first dose on measles vaccine effectiveness - A systematic review

BACKGROUND

In settings where measles has been eliminated, vaccine-derived immunity may in theory wane more rapidly due to a lack of immune boosting by circulating measles virus. We aimed to assess whether measles vaccine effectiveness (VE) waned over time, and if so, whether differentially in measles-eliminated and measles-endemic settings.

METHODS

We performed a systematic literature review of studies that reported VE and time since vaccination with measles-containing vaccine (MCV). We extracted information on case definition (clinical symptoms and/or laboratory diagnosis), method of vaccination status ascertainment (medical record or vaccine registry), as well as any biases which may have arisen from cold chain issues and a lack of an age at first dose of MCV. We then used linear regression to evaluate VE as a function of age at first dose of MCV and time since MCV.

RESULTS

After screening 14,782 citations, we identified three full-text articles from measles-eliminated settings and 33 articles from measles-endemic settings. In elimination settings, two-dose VE estimates increased as age at first dose of MCV increased and decreased as time since MCV increased; however, the small number of studies available limited interpretation. In measles-endemic settings, one-dose VE increased by 1.5% (95% CI 0.5, 2.5) for every month increase in age at first dose of MCV. We found no evidence of waning VE in endemic settings.

CONCLUSIONS

The paucity of data from measles-eliminated settings indicates that additional studies and approaches (such as studies using proxies including laboratory correlates of protection) are needed to answer the question of whether VE in measles-eliminated settings wanes. Age at first dose of MCV was the most important factor in determining VE. More VE studies need to be conducted in elimination settings, and standards should be developed for information collected and reported in such studies.

Measles outbreak from Hong Kong International Airport to the hospital due to secondary vaccine failure in healthcare workers

OBJECTIVE

To report an outbreak of measles with epidemiological link between Hong Kong International Airport (HKIA) and a hospital.

METHODS

Epidemiological investigations, patients' measles serology, and phylogenetic analysis of the hemagglutinin (H) and nucleoprotein (N) genes of measles virus isolates were conducted.

RESULTS

In total, 29 HKIA staff of diverse ranks and working locations were infected with measles within 1 month. Significantly fewer affected staff had history of travel than non-HKIA-related measles patients [10 of 29 (34.5%) vs 28 of 35 (80%); P < .01]. Of 9 airport staff who could recall detailed exposure history, 6 (66.7%) had visited self-service food premises at HKIA during the incubation period, where food trays, as observed during the epidemiological field investigation, were not washed after use. Furthermore, 1 airport baggage handler who was admitted to hospital A before rash onset infected 2 healthcare workers (HCWs) known to have 2 doses of MMR vaccination with positive measles IgG and lower viral loads in respiratory specimens. Infections in these 2 HCWs warranted contact tracing of another 168 persons (97 patients and 71 HCWs). Phylogenetic comparison of H and N gene sequences confirmed the clonality of outbreak strains.

CONCLUSION

Despite good herd immunity with overall seroprevalence of >95% against measles, major outbreaks of measles occurred among HKIA staff having daily contact with many international pssengers. Lessons from severe acute respiratory syndrome (SARS) and measles outbreaks suggested that an airport can be a strategic epidemic center. Pre-exanthem transmission of measles from airport staff to HCWs with secondary vaccine failure poses a grave challenge to hospital infection control.