Immunity to measles in young adults in Israel

Seroprevalence of measles, mumps and rubella among young adults, after 20 years of universal 2-dose MMR vaccination in Israel

Evidence-based vaccination policy is important for the global and local efforts of achieving control over measles. In 2007, the first Israeli birth cohort to be twice vaccinated during childhood with Measles-Mumps-Rubella vaccine reached adulthood. In parallel, Israel experienced its largest measles outbreak since 1994. We aimed to assess the seroprevalence of measles IgG antibodies and concordance with rubella and mumps seroprevalence among young Israeli adults born 1988-9 in comparison to previous birth cohorts, in order to inform evidence based prevention policy. We conducted a seroprevalence study of IgG antibodies among 439 Israeli adults born in 1988-9, based on a representative sample of sera collected at age 18-19 upon recruitment to mandatory military service in 2007. In total, 85.7% were seropositive for measles as compared with 95.6% in the 1996 recruitment (P < 0.001). The absolute decline was significant both for males (8.8%, P = 0.001) and females (12.1%, P < 0.001). There were no significant differences in seropositivity by gender, years of education, country of birth or smoking status. Rubella seropositivity among measles seropositives was 90.4%, significantly (P < 0.001) higher than 72.1% among measles seronegatives. Mumps seropositivity among measles seropositives was 87.0%, significantly (P < 0.001) higher than 62.3% among measles seronegatives. Results were similar for Israeli-born only. Our findings indicate that measles seroprevalence decreased after the last change in vaccination policy and reach sub-optimal level. Until global eradication is reached, a proactive vaccination program to supplement routine childhood vaccination program should be considered in Israel and in other countries.

Measles antibody prevalence rates among young adults in Israel

BACKGROUND

In Israel, vaccination coverage against measles is high, yet seroepidemiologic studies have shown that more than 15% of the 18-year-old population were unprotected against the disease. A 2-dose program of vaccination against measles, mumps, and rubella at the ages of 1 and 6 years was begun in 1990, supplemented by a measles catch-up plan for all 13-year-olds. The aim of this study was to assess the prevalence of antimeasles antibodies at induction to the Israel Defense Forces in the first doubly vaccinated birth-cohort.

METHODS

In 1996, serum samples of 540 recruits, 339 men and 201 women, were tested for measles virus antibody. Findings were compared with surveys conducted in 1987 and 1990.

RESULTS

Measles antibodies were present in 95.6% (95% CI, 93.5-97.1) of the recruits. Antibody prevalence was higher in women than in men (99% vs 93.5%; P =.0096). A slightly lower seroprevalence was found in recruits born in the former Soviet Union. The results were substantially higher than the seroprevalence rates found in 1987 (73.3%) and 1990 (84.6%).

CONCLUSIONS

The high prevalence of antimeasles antibodies in the young adult population in Israel points to the success of the double-vaccination policy in promoting immunity against the disease.

Measles epidemic in Israel-successful containment in the military

BACKGROUND

Measles vaccination at ages 12-15 months is a routine part of standard health care in developed countries. Nonetheless, the prevention and control of measles outbreaks remain a challenge, owing to incomplete or variable compliance with immunization programs and primary vaccine failure (approximately 5%). In Israel, vaccination coverage against measles is high, yet sero-epidemiological studies conducted in the early 1990s showed that 15% of 18-year-olds were unprotected.

METHODS

1994 there was a countrywide epidemic of measles, which spread to the military. The Israel Defense Forces Medical Corps immediately launched a wide-scale vaccination campaign, targeting primarily field units and training bases, where crowded living conditions are the rule.

RESULTS

The immunization campaign led to an abrupt cessation of morbidity in the military. In the civilian sector, where no intervention was undertaken, the epidemic continued for another 4 months.

CONCLUSIONS

Institutional measles outbreaks, especially in the presence of crowded conditions or high contact rates, may be effectively controlled by mass vaccination.

Measles immunity and response to revaccination of a young adult population in Israel

In order to evaluate the true immune status and the effect of revaccination on a young adult population, we collected serum samples from 289 military recruits who were vaccinated during an outbreak in 1991. Most vaccinees, age 18-25 years, had apparently been immunized once before as infants. Sera collected just prior to the vaccination and 14 and 28 days afterwards were tested for measles antibodies by hemagglutination inhibition (HI) and enzyme-linked immunosorbent assay (ELISA)-IgM. Before vaccination, 46 (15.9%) of the subjects had no HI antibodies, (< 1:4) and 48 (16.6%) had borderline (1:4) HI titer. Following vaccination, only ten (3.5%) remained negative and 19 (6.6%) had borderline titer. The increase in HI antibody titer was inversely proportional to the prevaccination titer, and 159 subjects (55.0%) showed no increase at all. The geometric mean titer (GMT) rose from 9.14 to 21.47. Among the prevaccination-negative subjects (HI < 1:4) 28 (60.9%) reached a postvaccination titer of > or = 1:8, and eight (17.4%) reached a titer of 1:4. Twelve (26.1%) of the negative subjects seroconverted and developed IgM, 16 (35%) seroconverted without IgM, and 18 (39%) remained negative and did not develop IgM. A group of eight vaccinees with prevaccination titer of > or = 1:4 developed IgM. Some were probably infected by the circulating wild-type virus prior to the vaccination. Thus, a total number of 20 of the 289 subjects studied (6.9%) had true negative preimmune status as judged by the IgM test. However, the vaccination campaign prevented further measles cases, apparently by increasing the population's immunity, particularly in individuals with very low titers or without measles antibodies.

Antibody response to measles vaccination in Turkish children

In recent years, there has been a remarkable increase in measles cases among preschool and secondary school children in Turkey, as in many other countries. The seroconversion and coverage rates of measles vaccine should therefore be evaluated in order to obtain data that could be used to determine the vaccination policy for Turkey. Measles immunity status was studied by an enzyme-linked immunosorbent (ELISA) test determining the anti-measles IgG antibody levels. Measles specific IgG antibodies were found to be positive in 77.88% of the entire study group of 800 children aged 11 months to 12 years, while 21.25% had negative sera. Seven (0.87%) subjects had borderline results. The results of this study indicate the need to administer a second dose of measles vaccine, preferably at 18 months of age concomitant with other vaccines. This vaccination policy, together with an increase in the extent of immunization coverage, may help to achieve the World Health Organization's (WHO) target of the complete eradication of measles.