Serological survey of measles immunity in the Czech Republic, 2013

Probability of exposure to the wild measles virus in adult population - Estimation from seroepidemiology and historical data

Vaccination against measles is one of the most effective public health interventions which has saved millions of lives and interrupted circulation of the natural virus in the population. However, it is widely accepted that the immunity after vaccination can wane, especially in those who have had no contact with the virus. This study aimed to classify the particular birth cohorts of adults with regard to their exposure to the wild measles virus in the population with a long history of mandatory vaccination. We introduced two methods. In the first, we estimated the probability of exposure to the wild virus through an analysis of antibody levels from the Immunologic Survey performed in the Slovak Republic in 2018, while the second was based on historical epidemiological data. Both methods resulted in similar estimations. Cohorts born in Slovakia before 1964 can be considered to be cohorts in which most people were exposed to the wild measles virus. Cohorts born after 1977 can be designated as cohorts that most likely did not come into the contact with the wild virus. Cohorts born between 1965 and 1976 are composed of a mixture, with a decreasing proportion of people exposed to the wild virus with increasing year of birth. The proposed methods can help identify potential immunity gaps in the adult population. They can be applied in other countries with high measles vaccination coverage to estimate the probability of exposure to the wild measles virus in particular birth cohorts.

Quantification of Waning Immunity After Measles Vaccination-Evidence From a Seroprevalence Study

We aimed to quantify rates of waning immunity after measles vaccination from seroprevalence data collected in a study of a population with high vaccination coverage and a fixed vaccination schedule. Data were collected during a national survey (the Immunological Survey) carried out in the Slovak Republic in 2018. The average rate of waning immunity against measles after the first dose of measles, mumps, and rubella (MMR) vaccine (ages 1.5-10 years) was 9.7% per year from the geometric mean titer value of 2,634 mUI/mL. The average waning rate after the second dose of MMR vaccine (ages 10-33 years) was significantly lower: 4.8% per year from the lower geometric mean titer of 1,331 mUI/mL. This decline in antibody levels suggests that vaccine-induced protection may be compromised and results in an increase in the proportion of seronegative/borderline individuals. These outcomes may provide a valuable source for critical assessment of direct and indirect effects of MMR vaccination.

Seroprevalence of Measles Antibodies in the Population of the Olomouc Region, Czech Republic—Comparison of the Results of Four Laboratories

Objectives: Although the incidence of measles has decreased globally since the introduction of regular vaccination, its frequency has increased again in recent years. The study is focused on data from the Olomouc Region in the Czech Republic analyzed in four laboratories. The obtained results were compared with already published data. Methods: The data were provided by individual laboratories in an anonymized form—age at the time of the examination, sex, and result of test. Samples were collected between June 2018 and September 2019 and evaluated on the scale positive–borderline–negative. Results: A total of 7962 sera samples were evaluated using three different methods—two types of ELISA tests and CLIA. Positive result was issued in a total of 62.6 percent of samples, but the results of individual laboratories varied widely from 55.5 to 70.8 percent. However, the same trend with the highest levels of antibodies in people born before beginning of vaccination was observed. Conclusions: Data show significantly different results depending on the individual laboratories and the detection kits used. The underestimation of the proportion of positive results can cause problems in selecting individuals for revaccination with a live vaccine, which may fail in weakly positive individuals.

Seropositivity of measles antibodies in the Israeli population prior to the nationwide 2018 - 2019 outbreak

Measles vaccine is administered in Israel as part of the routine childhood immunization program, at ages 1 and 6 years. In this study, we assessed seropositivity of the Israeli population against measles before the onset and propagation of the 2018-2019 measles outbreak. From the Israel Center for Disease Control National Serum Bank, 3,164 samples collected during 2015 were tested for measles antibodies. All the tests were performed using Enzyme-Linked Immunosorbent Assay (ELISA) commercial kit (Enzygnost, Anti-Measles Virus/IgG: Behring, Marburg, Germany). The overall seropositivity rate for measles was 90.7%. The seropositivity rate at 6 months and younger was 48.9%, and decreased to 3.8% among infants aged 6-11 months. Seropositivity increased to 90.7% in the 1-4-year age group, and reached 96.1% for 5-9 year-old children. Our results suggest high immunity in the Israeli population against measles virus, but not high enough to prevent outbreaks because of pockets of specific population groups with low immunization coverage. Infants between ages 6 and 11 months and children younger than 2 years had the lowest seropositivity rates being the age groups with the highest attack rates of measles during the epidemic of 2018. Efforts should be aimed at avoiding any delay in vaccination once a child reaches the age of 1 year and improving immunity levels in children aged 1-4 years.

A Serosurvey Identifying Vulnerability to Measles in Health Care Workers. A Hospital-Based Prospective Seroprevalence Study

The aim of this serological survey was to assess the persistence of measles antibodies among health care workers (HCWs) at risk of incidental measles. A prospective study of measles-specific antibodies in serum samples obtained from a total of 2782 participants aged 19-89 years was conducted between May 2018 and December 2019. The seropositivity rate of 93.7% (95% CI: 92.4-94.9%) in fully vaccinated participants aged 19-48 years was significantly lower than that of 98.0% (95% CI: 96.5-99.0%) in participants naturally immunised before 54 years. A cohort of those born in 1971-1975, vaccinated predominantly with one dose, showed lower seropositivity persistence (86.6%) than those fully vaccinated with two doses or naturally immunised. Otherwise, seropositivity was not markedly influenced by sex, age, smoking status, overweight, obesity or concomitant disease. The presence of sufficient antibody levels in a high proportion of HCWs irrespective of the way they acquired immunity is a favourable finding for managing incidental measles; hence, in the presence of a risk of a measles outbreak, it would be possible to perform targeted vaccination of only at-risk HCWs with a history of incomplete vaccination or missing information about the way in which immunity is acquired.

Seroprevalence of IgG antibodies against measles in a selected Polish population - do we need to be re-vaccinated?

Introduction

Measles is highly contagious, but preventable viral disease. Its outbreaks appear all over the world, and decreasing herd immunity excludes its elimination. High levels of IgG antibodies against a virus efficiently protects against infection.

Aim of this study

To assess the seroprevalence of anti-measles IgG in the serum of patients at different age levels tested for measles IgG at our laboratory.

Material and methods

The study was conducted from March to June of 2019. Retrospective analysis included results for measles-specific IgG from 364 tested patients. The age of enrolled subjects ranged from four months to 101 years, with a median age of 46, and a mean age of 43 ±18. Quantification of anti-measles IgG was performed using indirect chemiluminescence immunoassays on the DiaSorin Liaison® automated analyzer.

Results

Our results showed a seropositivity ratio of 78.02%. The lowest number of seropositive subjects was in the group of infants (0-1 years old), with a ratio of 53.85%, and the group of adults of 19-38 years old at 55.68%. The group of the oldest patients (70-101 years old) had the highest ratio of seropositive subjects (100%), while adults of 60-69 years old had a seropositivity ratio of 97.22%.

Conclusions

These data suggest that the group of young adults who were vaccinated with one or two doses of MMR vaccine in childhood are the most susceptible for infection, and when working in contact with other people, should be re-vaccinated for protection against measles.

Antibodies against measles and rubella virus among different age groups in Thailand: A population-based serological survey

Measles and rubella are highly contagious viral diseases transmitted via respiratory secretions and aerosolized droplets. Thailand has implemented universal vaccination against measles using the monovalent measles (M) or the trivalent measles-mumps-rubella (MMR) vaccine for the past 30 years. Nevertheless, incidence of measles and rubella remains in some parts of the country. We conducted a seroprevalence study to evaluate the antibodies to measles and rubella virus among Thais of all ages and to determine pre-existing immunity resulting from either vaccination and/or natural exposure. A total of 1,781 serum samples collected in 2014 was tested for IgG to measles and rubella virus by commercial enzyme-linked immunosorbent assays (ELISA). Percentages of individuals with protective antibody levels and the geometric mean concentrations (GMC) of IgG in each age group were analysed. The GMC of anti-measles IgG and anti-rubella IgG were 653.7 IU/L (95% confidence interval (CI); 555.9–751.4) and 39.5 IU/mL (95% CI;35.0–43.9), respectively. Thais between the ages of six months and 25 years did not demonstrate sufficient protective herd immunity for measles. This observation is consistent with the recent measles outbreaks in this age group. Lower prevalence of immunity against rubella was found among children ages 5–6 years who may not have completed vaccination as infants. Our findings identify gaps in rubella and measles immunity in specific age groups and support recommendations for catch-up MMR vaccination in individuals 30 years of age or younger.

Combining serological and contact data to derive target immunity levels for achieving and maintaining measles elimination

BACKGROUND

Vaccination has reduced the global incidence of measles to the lowest rates in history. However, local interruption of measles virus transmission requires sustained high levels of population immunity that can be challenging to achieve and maintain. The herd immunity threshold for measles is typically stipulated at 90-95%. This figure does not easily translate into age-specific immunity levels required to interrupt transmission. Previous estimates of such levels were based on speculative contact patterns based on historical data from high-income countries. The aim of this study was to determine age-specific immunity levels that would ensure elimination of measles when taking into account empirically observed contact patterns.

METHODS

We combined estimated immunity levels from serological data in 17 countries with studies of age-specific mixing patterns to derive contact-adjusted immunity levels. We then compared these to case data from the 10 years following the seroprevalence studies to establish a contact-adjusted immunity threshold for elimination. We lastly combined a range of hypothetical immunity profiles with contact data from a wide range of socioeconomic and demographic settings to determine whether they would be sufficient for elimination.

RESULTS

We found that contact-adjusted immunity levels were able to predict whether countries would experience outbreaks in the decade following the serological studies in about 70% of countries. The corresponding threshold level of contact-adjusted immunity was found to be 93%, corresponding to an average basic reproduction number of approximately 14. Testing different scenarios of immunity with this threshold level using contact studies from around the world, we found that 95% immunity would have to be achieved by the age of five and maintained across older age groups to guarantee elimination. This reflects a greater level of immunity required in 5-9-year-olds than established previously.

CONCLUSIONS

The immunity levels we found necessary for measles elimination are higher than previous guidance. The importance of achieving high immunity levels in 5-9-year-olds presents both a challenge and an opportunity. While such high levels can be difficult to achieve, school entry provides an opportunity to ensure sufficient vaccination coverage. Combined with observations of contact patterns, further national and sub-national serological studies could serve to highlight key gaps in immunity that need to be filled in order to achieve national and regional measles elimination.