Evaluation of nationwide supplementary immunization in Lao People's Democratic Republic: Population-based seroprevalence survey of anti-measles and anti-rubella IgG in children and adults, mathematical modelling and a stability testing of the vaccine

Abstract

BackgroundMeasles outbreaks have occurred in some countries despite supplementary immunization activities (SIA) using measles-containing vaccine with high vaccination coverage. We conducted a cross-sectional seroprevalence survey to estimate population immunity in Lao People's Democratic Republic where repeated mass immunization has failed to eliminate measles.Methods and findingsIn this nationwide multistage cluster sampling survey conducted in 2014 based on probability proportionate to size sampling, blood samples were collected from 2,135 children and adults living in 52 randomly selected villages. Anti-measles and anti-rubella IgG were measured, and IgG prevalence was calculated. We applied mathematical modelling to estimate the number of cases of congenital rubella syndrome (CRS) in 2013 that were averted by the 2011 SIA. A stability testing was applied to the MR vaccine at 4°C, 25°C, and 35°C to examine stability differences between measles and rubella vaccine components. Measles IgG prevalence was significantly lower in the target age groups (5–21 years) of the 2011 SIA using a combination vaccine for measles and rubella vaccine (MR vaccine) than in young adults (22–39 years) (86.8% [95% CI: 83.0–90.6] vs. 99.0% [98.3–99.8]; p<0.001), whereas rubella IgG prevalence was significantly higher (88.2% [84.5–91.8] vs. 74.6% [70.7–78.5]; p<0.001). In the SIA target age groups, prevalence of measles IgG, but not rubella IgG, increased with age. CRS cases prevented in 2013 ranged from 16 [0–50] to 92 [32–180] if the force of infection had remained unchanged or had been reduced by 75%, respectively. In freeze-dried conditions, the measles vaccine component was more heat sensitive than the rubella component.ConclusionsInconsistent IgG prevalence between measles and rubella in Lao PDR can be partly explained by different stability of the measles and rubella vaccine components under heat exposure. Suboptimal vaccine handling may cause insufficient immunogenicity for measles, which subsequently leads to an outbreak despite high SIA coverage, while direct evidence is lacking. Temperature monitoring of the vaccine should be conducted.

Factors influencing basic vaccination coverage in Myanmar: secondary analysis of 2015 Myanmar demographic and health survey data

“…The present study also failed to evaluate regional variations in complete vaccination coverage, as the small number of children in each state/region would have produced a low statistical power. Moreover, other countries have had discrepancies between the vaccination coverage rate and population-level immunity for vaccine-preventable diseases, which may be related to insufficient cold chain control and the vaccine’s heat sensitivity [39]. Thus, to evaluate the risks of related outbreaks, direct immunity assessment is needed (e.g., seroepidemiological analysis).…”

Estimating the immunogenicity of measles-rubella vaccination administered during a mass campaign in Lao People’s Democratic Republic using multi-valent seroprevalence data

“…Despite levels of coverage reported for measles vaccination of above the herd immunity threshold (the coverage required to control transmission 3 ), measles outbreaks continue to occur in some countries. In Lao PDR, for example, supplemental immunization campaigns (SIAs) of measles and the measles-rubella vaccine reported coverage of 96% in 2007 and 97% in 2011 respectively, targeting wide age ranges (children aged 9 months-14 years and 9 months – 19 years respectively), and outbreaks were reported in 2012, 2013 and 2014 4 . The factors contributing to these ongoing outbreaks are poorly understood, but need to be elucidated if targets specified in the Global Vaccine Action Plan of measles elimination in 5 world regions by 2020 5 are to be achieved.…”

Population immunity to measles, rubella, mumps, and varicella among adults in Khanh Hoa province, Socialist Republic of Vietnam; residual sample analysis from multistage cluster sampling survey

“…A previous study in Vietnam found marked discrepancies between estimated levels of population protection and vaccine coverages of measles [5]. Reported immunization coverage does not necessarily offer reliable information with which to estimate population immunity [12,21,22].…”

“…As the sampling design of the present study was derived from other purposes, comparison with results from different times (past and future) and different places (regions in Vietnam and other countries) is di cult. To reveal the current population immunity and to contribute to the formulation of immunization policy, more samples (i.e., ≥2,000 samples) from wider geographical areas are needed [12,21].…”

“…Third, the present study did not include a pediatric population (< 20 years old), so virus circulation, particularly for the most affected age stratum, was di cult to estimate. Age-speci c IgG prevalence in the younger population may provide more accurate estimation of virus circulation [21,22], and allow us to calculate the force of infection for each disease in local settings. The present residual serum sample analysis is regarded as a pilot study, and a population-based seroprevalence survey covering both children and adults in wider geographical areas is needed to evaluate population immunity in Vietnam.…”