Assessing the impact of COVID-19 on routine immunization in Sierra Leone.

BACKGROUND: The COVID-19 pandemic had a profound impact on healthcare systems and services, including routine immunization (RI). To date, there is limited information on the effects of the COVID-19 pandemic on RI in West African countries such as Sierra Leone, which had already experienced public health emergencies that disrupted its healthcare system. Here, we describe the impact of the COVID-19 pandemic on the RI of key antigens in Sierra Leone. METHODS: We used vaccination data from the District Health Information System for BCG, measles-rubella 1 and 2, and pentavalent 1 and 3 antigens. We compared 2019, 2020, 2021, and 2022 annual coverage rates for the selected antigens at the national and district levels. We used the Pearson chi-square test to assess the difference between annual coverage rates between 2019 and 2020, 2020-2021, and 2021-2022. RESULTS: National coverage rates for all antigens declined in 2019-2020, notably measles-rubella 1 and pentavalent 3 (-5.4% and - 4.9%). Between 2020 and 2021, there was an overall increase in coverage (+ 0.2% to + 2.5%), except for measles-rubella 2 (-1.8%). Measles-rubella antigens rebounded in 2021-2022, while others decreased between - 0.5 and - 1.9% in coverage. Overall, all district-level coverage rates in 2022 were lower than those in 2019. Most districts decreased between 2019 and 2022, though a few had a continuous increase; some had an increase/recovery between 2020 and 2021; some districts had recovered 2019 levels by 2022. CONCLUSION: The COVID-19 pandemic impacted Sierra Leone's national BCG, measles-rubella, and pentavalent antigen immunization, which were not fully restored in 2022. Most districts experienced notable coverage declines during the pandemic, though a few reached or surpassed 2019 rates in 2022. Examining pandemic impact can benefit from a focus beyond the national level to identify vulnerable regions. Sierra Leone's post-pandemic RI reestablishment needs targeted strategies and continual investments for equitable access and coverage, as well as to prevent vaccine-preventable diseases.

Regional disparities in measles vaccination coverage and their associated factors: an ecological study in Japan.

BACKGROUND: The decline in measles vaccination coverage is a global concern. In Japan, coverage of the first-dose of measles vaccine, which had exceeded the target of 95.0% since fiscal year (FY) 2010, fell to 93.5% in FY 2021. Vaccination coverage increased to 95.4% in FY 2022 but varied by municipality. Few studies have focused on regional disparities in measles vaccination coverage. This study aimed to clarify the regional disparities in measles vaccination coverage by municipality in Japan and their associated factors. METHODS: In this ecological study, the measles vaccination coverage in FY 2022; population density; area deprivation index (ADI, an indicator of socioeconomic status); proportion of foreign nationals, single-father households, single-mother households, and mothers aged ≥30 years; and number of medical facilities, pediatricians, and non-pediatric medical doctors in 1,698 municipalities were extracted from Japanese government statistics. Negative binomial regression was performed with the number of children vaccinated against measles as the dependent variable, number of children eligible for measles vaccination as the offset term, and other factors as independent variables. RESULTS: Vaccination coverage was less than 95.0% in 54.3% of municipalities. Vaccination coverage was significantly positively associated with population density and negatively associated with the proportion of single-father households, mothers aged ≥30 years, and the ADI (incidence rate ratio [IRR]: 1.004, 0.976, 0.999, 0.970, respectively). CONCLUSION: This study showed regional disparities in measles vaccination coverage in Japan. Single-father households, age of mothers, and socioeconomic status may be key factors when municipalities consider strategies to improve vaccination coverage.

Evaluation of the sensitivity of a measles diagnostic real-time RT-PCR assay incorporating recently observed priming mismatch variants, 2024.

We investigated a variant of measles virus that encodes three mismatches to the reverse priming site for a widely used diagnostic real-time RT-PCR assay; reduction of sensitivity was hypothesised. We examined performance of the assay in context of the variant using in silico data, synthetic RNA templates and clinical specimens. Sensitivity was reduced observed at low copy numbers for templates encoding the variant sequence. We designed and tested an alternate priming strategy, rescuing the sensitivity of the assay.

Modeling measles transmission in adults and children: Implications to vaccination for eradication.

Despite the availability of successful vaccines, measles outbreaks have occurred frequently in recent years, presumably due to the lack of proper vaccination implementation. Moreover, measles cases in adult groups, albeit small in number, indicate that the previously neglected adult group may need to be brought into vaccine coverage to achieve WHO's goal of measles eradication from the globe. In this study, we develop a novel transmission dynamics model to describe measles cases in adults and children to evaluate the role of adult infection in persistent measles cases and vaccination programs for eradication. Analysis of our model, validated by measles cases from outbreaks in Nepal, provides the vaccination reproduction number (conditions for measles eradication or persistence) and the role of contact network size. Our results highlight that while children are primary targets for measles outbreaks, a small number of infections in adults may act as a reservoir for measles, causing obstacles to eradication. Furthermore, our model analysis shows that while impactful controls can be achieved by children-focused vaccines, a combined adult-child vaccination program may help assert eradication of the disease.

Relationship between parental acceptance of the COVID-19 vaccine and attitudes towards measles vaccination for children: A cross-sectional study.

BACKGROUND: The COVID-19 pandemic has led to decreased measles vaccination rates globally, exacerbating vaccine hesitancy. This study examines the relationship between COVID-19 vaccine acceptance and childhood measles vaccination among parents in Hong Kong. METHODS: A cross-sectional online survey was conducted in Hong Kong from March to September 2022. Parents were recruited via the Qualtrics panel, and a total of 588 parents were invited via email or social media account to participate in the survey. We used the adjusted Measles-containing Vaccine Hesitancy Scale for the assessment of parental vaccine hesitancy for children. A multiple linear regression analysis was conducted to examine the association between parental acceptance of the COVID-19 vaccine and their attitudes towards childhood measles vaccination. RESULTS: Of the 588 participants, parents who have been vaccinated against COVID-19 exhibited significantly less measles-containing vaccine hesitancy comparing to those unvaccinated (ß = -2.96, 95% confidence interval [CI]: -5.10 to -0.83, p = 0.007). Mothers exhibited more hesitancy compared to fathers (ß = 1.64, 95% CI: 0.60 to 2.68, p = 0.002). Parents with a higher self-rated health (ß = -2.20, 95% CI: -3.21 to -1.20, p < 0.001), or who have received advice from health professionals to offer measles, influenza, or COVID-19 vaccines for kids (ß = -2.41, 95% CI: -3.49 to -1.32, p < 0.001) had lower levels of hesitancy. CONCLUSION: COVID-19 vaccine status of parents was associated with reduced hesitancy towards measles vaccines for their children. Addressing vaccine hesitancy effectively requires targeted communication strategies, particularly focusing on those unvaccinated and leveraging the influence of healthcare professionals.

"If the nurse tells me this is a good thing, I trust her completely" - Exploring health system enablers of MMR vaccine uptake in the Finnish Somali community: A mixed method study.

BACKGROUND: Globally, migrant populations usually experience lower vaccine coverage than the general population. In Finland, the MMR vaccination coverage of Somalis has not been studied specifically, but existing evidence suggests that the MMR vaccination coverage is high. The aim of this study was to examine both vaccination coverage of Somali children and factors associated with the MMR vaccine uptake of Somali children living in Finland. METHODS: Twenty-seven mothers and seventeen public health nurses were interviewed using a semi-structured interview protocol. Audio-recorded interviews were transcribed and translated and analysed thematically after coding. The personal identity code of Somali children born in 2015 and 2020 were extracted from the Population Information System (PIS), and their vaccination coverage data was extracted from the national vaccination register (NVR) to calculate MMR vaccination coverage for Somali children. RESULTS: 96 % of Somali children born in 2015 and 81 % of those born in 2020 received their MMR vaccination. In contrast, the national average MMR vaccine uptake for children born in 2015 was 95 %, while 94 % of those born in 2020 were vaccinated against MMR. Somali mothers had poor knowledge of the MMR vaccine and the diseases it protects against. Trust towards the Finnish healthcare system, perceived benefits of vaccinating, positive attitudes towards vaccines, nurses' systematic approach to vaccine introduction, and nurses taking into account the cultural background of the clients were recognised as enablers positively affecting MMR vaccination uptake. CONCLUSION: Despite limited knowledge of vaccines, Somali immigrant mothers believe in the benefits of vaccination, and they displayed strong trust towards public health nurses. Further investigation is needed to understand why MMR vaccination coverage has declined among the younger Somali population.

Evaluating Scope and Bias of Population-Level Measles Serosurveys: A Systematized Review and Bias Assessment.

BACKGROUND: Measles seroprevalence data have potential to be a useful tool for understanding transmission dynamics and for decision making efforts to strengthen immunization programs. In this study, we conducted a systematized review and bias assessment of all primary data on measles seroprevalence in low- and middle-income countries (as defined by World Bank 2021 income classifications) published from 1962 to 2021. METHODS: On 9 March 2022, we searched PubMed for all available data. We included studies containing primary data on measles seroprevalence and excluded studies if they were clinical trials or brief reports, from only health-care workers, suspected measles cases, or only vaccinated persons. We extracted all available information on measles seroprevalence, study design, and seroassay protocol. We conducted a bias assessment based on multiple categories and classified each study as having low, moderate, severe, or critical bias. This review was registered with PROSPERO (CRD42022326075). RESULTS: We identified 221 relevant studies across all World Health Organization regions, decades, and unique age ranges. The overall crude mean seroprevalence across all studies was 78.0% (SD: 19.3%), and the median seroprevalence was 84.0% (IQR: 72.8-91.7%). We classified 80 (36.2%) studies as having severe or critical overall bias. Studies from country-years with lower measles vaccine coverage or higher measles incidence had higher overall bias. CONCLUSIONS: While many studies have substantial underlying bias, many studies still provide some insights or data that could be used to inform modelling efforts to examine measles dynamics and programmatic decisions to reduce measles susceptibility.

The Case for Assessing the Drivers of Measles Vaccine Uptake.

Global measles cases are on the rise following disruptions to routine immunisation programs during the COVID-19 pandemic, with devastating consequences. According to the World Health Organization, the behavioural and social drivers of vaccination include what people think and feel about vaccines, social processes, motivation to vaccinate and practical barriers to vaccination. However, the drivers of measles vaccine uptake are not necessarily the same as those for other childhood vaccines, and we lack data on how these drivers specifically have changed during and since the COVID-19 pandemic. Without accurately measuring the behavioural and social drivers for measles vaccination, and ideally measuring them serially over time, countries cannot design, target and implement interventions that effectively increase and sustain measles vaccine coverage. This paper outlines what is and is not known about the behavioural and social drivers of measles vaccination and provides recommendations for improving their post-pandemic assessment.

A World without Measles and Rubella: Addressing the Challenge of Vaccine Hesitancy.

The worldwide elimination of measles and rubella is feasible, but not without overcoming the substantial challenge of vaccine hesitancy. This challenge is complicated by the spread of misinformation and disinformation fueled by rapidly progressing technologies and evolving forms of online communication. The recent COVID-19 pandemic has only added further complexity to this challenge. However, considerable progress has been made in understanding the scope of the problem and the complex factors that influence vaccine hesitancy. Our understanding of evidence-based strategies for addressing vaccine hesitancy has grown significantly, including evidence for effective communication and behavioral interventions. In this article, we review measles and rubella vaccines and vaccine hesitancy. We then provide an overview of evidence-based strategies for addressing vaccine hesitancy, including communication strategies and behavioral interventions. This article is relevant to healthcare professionals, health system leaders, public health professionals, policymakers, community leaders, and any individuals who have a role in addressing vaccine hesitancy in their communities. Finally, we review future directions and major areas of research need.

Sustaining the Elimination of Measles, Rubella and Congenital Rubella Syndrome in the Americas, 2019-2023: From Challenges to Opportunities.

This report reviews national data from all Member States on measles, rubella, and congenital rubella syndrome (CRS) elimination in the Region of the Americas during 2019-2023. It includes an analysis of compliance with vaccination coverage, surveillance indicators, and measles outbreaks, as well as an analysis of the response capacity of the laboratory network and a country case study that meets all indicators. The sources of information were the integrated epidemiological surveillance system for measles and rubella of the Pan American Health Organization (PAHO)/World Health Organization (WHO) and the Joint Reporting Form (eJRF), among others. From 2020 to 2022, regional coverage with first (MMR-1) and second doses (MMR-2) decreased to rates below 90%. The regional suspected case notification rate was maintained above the minimum expected 2.0 suspect cases per 100,000 population, except in 2021. During 2019 to 2023, 18 countries experienced outbreaks, with two of the outbreaks resulting in re-established endemic transmission. In conclusion, two countries in the Americas have not maintained measles elimination, but by the end of 2023 no country showed endemic measles transmission. One of the countries that lost its certification of elimination in 2018 managed to be reverified in 2023; the other is pending reverification. All countries maintained rubella elimination. Despite these challenges, the sustainability of the elimination of these diseases remains a health priority in the Region.

Breakthrough Measles among Vaccinated Adults Born during the Post-Soviet Transition Period in Mongolia.

Mongolia experienced a nationwide measles outbreak during 1 March 2015-31 December 2016, with 49,077 cases reported to the WHO; many were among vaccinated young adults, suggesting a possible role of vaccine failure. Advanced laboratory methods, coupled with detailed epidemiological investigations, can help classify cases as vaccine failure, failure to vaccinate, or both. In this report, we conducted a study of cases to identify risk factors for breakthrough infection for a subset of laboratory-confirmed measles cases. Of the 193 cases analyzed, only 19 (9.8%) reported measles vaccination history, and 170 (88%) were uncertain. Measles-specific IgG avidity testing classified 120 (62%) cases as low IgG avidity, indicating no prior exposure to measles. Ten of these cases with low IgG avidity had a history of measles vaccination, indicating primary vaccine failure. Overall, sixty cases (31%) had high IgG avidity, indicating breakthrough infection after prior exposure to measles antigen through vaccination or natural infection, but the IgG avidity results were highly age-dependent. This study found that among young children aged 9 months-5 years, breakthrough infection was rare (4/82, 5%); however, among young adults aged 15-25 years, breakthrough infection due to secondary vaccine failure (SVF) occurred on a large scale during this outbreak, accounting for the majority of cases (42/69 cases, 61%). The study found that large-scale secondary vaccine failure occurred in Mongolia, which highlights the potential for sustained outbreaks in post-elimination settings due to "hidden" cohorts of young adults who may have experienced waning immunity. This phenomenon may have implications for the sustainability of measles elimination in countries that remain vulnerable to the importation of the virus from areas where it is still endemic. Until global measles elimination is achieved, enhanced surveillance and preparedness for future outbreaks in post- or peri-elimination countries may be required.

Evolution and Contribution of a Global Partnership against Measles and Rubella, 2001-2023.

This article describes the arc of global measles and rubella elimination since 2000 from the perspective of the founding partners of the Measles Initiative. The Measles Initiative was formed in 2001 as a partnership among the American Red Cross, the Centers for Disease Control and Prevention, UNICEF, the United Nations Foundation, and the World Health Organization with the aim to reduce measles deaths in low-income countries. Recognizing rubella as the leading infectious disease cause of congenital abnormalities globally and achievement of measles and rubella elimination in the region of the Americas, the partnership was renamed the Measles and Rubella Initiative (MRI) in 2012. The goals of the MRI were at least a 95% reduction in global measles mortality and elimination of measles and rubella in at least five of the six WHO regions. In January 2023, the membership of the partnership was expanded to include the Bill and Melinda Gates Foundation (BMGF) and Gavi the Vaccine Alliance, and its name changed to the IA2030 Measles and Rubella Partnership. We describe the role the partnership has had in measles partner effectiveness and its impact on measles and rubella disease burden, including how the partnership has strategically adapted to the evolving immunization landscape. We conclude with lessons learned regarding the role global partnerships can play in furthering the impact of disease control programs within the current global immunization environment.

Accelerating Global Measles and Rubella Eradication-Saving Millions of Lives, Preventing Disability, and Averting the Next Pandemic.

No vaccine has been more effective in reducing disease burden, especially in preventing child deaths, than measles-containing vaccine. The return on investment makes measles-containing vaccine one of the most cost-effective public health measures available. Exhaustive reviews of biological, technical, economic and programmatic evidence have concluded that measles can and should be eradicated, and by including rubella antigen in measles-containing vaccine, congenital rubella syndrome will also be eradicated. All World Health Organisation Regions have pledged to achieve measles elimination. Unfortunately, not all countries and global partners have demonstrated an appropriate commitment to these laudable public health goals, and the negative impact of the COVID-19 pandemic on coverage rates has been profound. Unsurprisingly, large disruptive outbreaks are already occurring in many countries with a global epidemic curve ominously similar to that of 2018/2019 emerging. The Immunization Agenda 2030 will fail dismally unless measles and rubella eradication efforts are accelerated. Over half of all member states have been verified to have eliminated rubella and endemic rubella transmission has not been re-established in any country to date. In 2023, 84 countries and areas were verified to have sustained elimination of measles. However, without a global target, this success will be difficult to sustain. Now is the time for a global eradication goal and commitment by the World Health Assembly. Having a galvanising goal, with a shared call for action, will demand adequate resourcing from every country government and global partners. Greater coordination across countries and regions will be necessary. Measles, rubella and congenital rubella syndrome eradication should not remain just a technically feasible possibility but rather be completed to ensure that future generations of children do not live under the shadow of preventable childhood death and lifelong disability.

Progress and Challenges in Measles and Rubella Elimination in the WHO European Region.

The elimination of both measles and rubella remains a priority for all 53 Member States of the World Health Organization (WHO) European Region. To provide an update on the epidemiological status of measles and rubella in the Region, we reviewed surveillance data on both diseases for 2023 submitted monthly by national surveillance institutions. We analyzed the cases of measles and rubella for 2023 by age group, case classification, vaccination, hospitalization, and importation status and report on measles-related deaths. In 2023, 60,860 measles cases, including 13 fatal cases, were reported in 41 countries. Most cases (95%; n = 57,584) were reported by six countries: Azerbaijan, Kazakhstan, Kyrgyzstan, Romania, the Russian Federation, and Türkiye. Of the 60,848 cases with data on age, 19,137 (31%) were 1-4 years old and 12,838 (21%) were 5-9 years old. A total of 10,412 (17%) were 20 years and older. The genotypes identified in the Region were largely dominated by D8 variants (n = 1357) and the remainder were B3 variants (n = 221). In 2023, 345 rubella cases were reported by 17 countries, mostly from Poland, Kyrgyzstan, Tajikistan, Türkiye, and Ukraine. A total of 262 cases (76%) were classified as clinically compatible and 79 (23%) were laboratory-confirmed. To achieve the elimination of measles and rubella in the Region, political commitment needs to be revived to enable urgent efforts to increase vaccination coverage, improve surveillance and outbreak preparedness, and respond immediately to outbreaks.

Measles and Rubella Diagnostic and Classification Challenges in Near- and Post-Elimination Countries.

Measles and rubella are vaccine-preventable viral diseases and can be prevented by safe, highly effective vaccination with measles- and rubella-containing vaccines. Given the myriad causes of febrile exanthems, laboratory surveillance for both measles and rubella is important to document the incidence of these diseases and to track the progress and maintenance of elimination in near- and post-elimination settings. Diagnostic challenges can hinder effective surveillance and classification challenges can hinder efforts to demonstrate achievement or maintenance of elimination. In this report, we review diagnostic and classification challenges for measles and rubella in near- and post-elimination settings.

Epidemiology of measles in southern Iran: trends, challenges, and vaccination insights.

Background: Measles, a highly contagious and vaccine-preventable disease, continues to present global public health challenges. This retrospective study focused on measles outbreaks in Hormozgan province, southern Iran, spanning from 2014 to 2019. Methods: Between 2014 and 2019, patients suspected of having measles, as reported by medical centers in Hormozgan, were subject to a comprehensive evaluation. The diagnosis of measles was conclusively established through the use of real-time polymerase chain reaction (RT-PCR) testing. A detailed collection of pertinent data was undertaken. SPSS software, version 21, was employed for statistical analysis. Results: In the current study, out of 1291 clinically suspected measles cases, 151 were PCR-confirmed, with an average age of 16.77 years (±10.46), comprising 50.9% males and 49.1% females. The annual distribution showed varied incidence: 8.4% in 2014, peaking at 18.8% in 2015, then fluctuating to 11.4% in 2016, 0.8% in 2017, and 17.9% in 2018, with no cases in 2019. Among confirmed cases, 16.5% were vaccinated, while 68.2% were not, and 15.23% had unknown vaccination status. Conclusion: This retrospective study highlights the ongoing challenge of measles in Hormozgan province, Iran, from 2014 to 2019. Despite measles being preventable by vaccination, a significant number of cases were confirmed among both vaccinated and unvaccinated individuals, indicating gaps in immunization coverage and effectiveness. The fluctuating annual incidence, with a peak in 2015 and no cases in 2019, suggests variable success in disease control efforts. This underscores the need for enhanced surveillance, improved vaccination strategies, and public health interventions to effectively combat measles outbreaks in this region.

Spatio-temporal pattern and associate meteorological factors of airborne diseases in Bangladesh using geospatial mapping and spatial regression model.

Background and Aims: Airborne diseases due to climate change pose significant public health challenges in Bangladesh. Little was known about the spatio-temporal pattern of airborne diseases at the district level in the country. Therefore, this study aimed to investigate the spatio-temporal pattern and associated meteorological factors of airborne diseases in Bangladesh using exploratory analysis and spatial regression models. Methods: This study used district-level reported cases of airborne diseases (meningococcal, measles, mumps, influenza, tuberculosis, and encephalitis) and meteorological data (temperature, relative humidity, wind speed, and precipitation) from 2017 to 2020. Geospatial mapping and spatial error regression models were utilized to analyze the data. Results: From 2017 to 2020, a total of 315 meningococcal, 5159 measles, 1341 mumps, 346 influenza, 4664 tuberculosis, and 229 encephalitis cases were reported in Bangladesh. Among airborne diseases, measles demonstrated the highest prevalence, featuring a higher incidence rate in the coastal Bangladeshi districts of Lakshmipur, Patuakhali, and Cox's Bazar, as well as in Maulvibazar and Bandarban districts from 2017 to 2020. In contrast, tuberculosis (TB) emerged as the second most prevalent disease, with a higher incidence rate observed in districts such as Khagrachhari, Rajshahi, Tangail, Bogra, and Sherpur. The spatial error regression model revealed that among climate variables, mean (ß = 9.56, standard error [SE]: 3.48) and maximum temperature (ß = 1.19, SE: 0.40) were significant risk factors for airborne diseases in Bangladesh. Maximum temperature positively influenced measles (ß = 2.74, SE: 1.39), whereas mean temperature positively influenced both meningococcal (ß = 5.57, SE: 2.50) and mumps (ß = 11.99, SE: 3.13) diseases. Conclusion: The findings from the study provide insights for planning early warning, prevention, and control strategies to combat airborne diseases in Bangladesh and similar endemic countries. Preventive measures and enhanced monitoring should be taken in some high-risk districts for airborne diseases in the country.

Phase III, open-label, single-arm study of a new MMR vaccine (JVC-001); measles AIK-C, mumps RIT 4385, rubella Takahashi, as a second vaccine dose in healthy Japanese children aged 5-6 years.

PURPOSE: This Phase III, multicenter, open-label, single-arm study evaluated the safety and immunogenicity of the measles-mumps-rubella (MMR) combined vaccine, JVC-001, as a second MMR vaccination. METHODS: Healthy Japanese children aged 5-6 years received a single dose of JVC-001 following a first measles, mumps, and rubella vaccination (measles-rubella bivalent and mumps monovalent vaccine [Hoshino or Torii strain] or JVC-001) or the MMR vaccine received between ages 1 to <4 years. Immunogenicity was evaluated using antibody titers before and after vaccination (Day 1/Day 43). The primary endpoint was the seroprotection rate of antibody titers against each virus; geometric mean titer (GMT) was also evaluated. Adverse events (AEs) and adverse drug reactions (ADRs) were monitored. RESULTS: One-hundred participants completed the study. The seroprotection rate of antibody titers against measles, rubella, and mumps virus (genotype D) were 100.0% (95% confidence interval [CI] 96.4%, 100.0%), 100.0% (95% CI 96.4%, 100.0%), and 100.0% (95% CI 96.3%, 100.0%), respectively. GMT (fold) increases (Day 1 to Day 43) were 16.0 to 55.7 for measles virus, 35.5 to 99.0 for rubella virus, and 25.7 to 89.5 for mumps virus (genotype D). Solicited ADRs occurred in 40.0% of participants (injection site, 34.0%; systemic, 13.0%). CONCLUSIONS: The second MMR vaccination with JVC-001 demonstrated sufficient antibody coverage against all three viruses; the safety profile was tolerable. CLINICAL TRIAL REGISTRATION: jRCT2080225022.

Seroepidemiology of measles and rubella among Hong Kong young adults and the humoral responses of an MMR booster among participants with low antibody levels.

BACKGROUND: Some individuals may not retain adequate immunity against measles and rubella years after two doses of measles, mumps, and rubella (MMR) vaccination due to vaccine failure. This study aimed to investigate the rates of vaccine failure and seroconversion by administering an MMR booster to young adults. METHODS: We first assessed measles and rubella antibody levels using the Luminex multiplex assay, VIDAS IgG assay, and plaque reduction neutralization test (PRNT) among individuals aged 18-30 years old who had received two doses of MMR vaccine. Participants with low measles and/or rubella antibody levels as confirmed by VIDAS received an MMR booster. Antibody levels were measured at 1-month post-booster. RESULTS: Among 791 participants, the measles and rubella seroprevalence rates were 94.7% (95% CI: 92.9%-96.0%) and 97.3% (95% CI: 96.0%-98.3%), respectively. Lower seroprevalence rates were observed among older participants. 113 participants who received an MMR booster acquired higher measles and rubella antibody levels at 1-month post-booster compared to baseline. CONCLUSIONS: Although measles and rubella vaccine failures were observed among 5.3% and 2.7% of young adults, respectively, an MMR booster triggered a significant antibody response.