Title : Evaluation of the national immunization program by estimating immunoglobulin G antibody prevalence of measles and rubella in Lao People's Democratic Republic
Abstract:
Objective: To eliminate measles and rubella, it is critical to develop strategic and efficient immunization programs. This study aimed to evaluate the population immunity and the measles-rubella program's effectiveness by estimating anti-measles and anti-rubella IgG prevalence in the general population of the Lao People's Democratic Republic (PDR).
Methods: A nationwide seroprevalence survey was conducted in Lao PDR between May and June 2019, using the multi-stage cluster sampling method. In the first and second stages, 26 districts and two villages from each province were selected using probability proportional to size sampling. In the third stage, 42 people were randomly selected [DW(3] [T4] from the residents' list in each village. Dried blood spot samples were collected onto WhatmanTM 903 filter paper by finger prick. IgG titers were measured by EnzygnostR enzyme-linked immunosorbent assay, and the results were considered positive at ≥120 mIU/ml for measles and ≥ 10 IU/ml for rubella.
Results: We approached one thousand nine hundred people and enrolled ninety-three subject (females: 53.0%, mean age: 23.1 years (1-89 years)), excluding those with inappropriate specimens, were included in the analysis. IgG prevalence was estimated to be 98.3% [95% CI: 97.7-98.8] for measles and 87.8% [86.4-89.2] for rubella. Measles IgG prevalence was estimated to be greater than 95% except for those aged 1-2 years, and rubella was estimated to be greater than 80% except for those aged 1-2 years and 25-34 years.
Conclusions: Overall, IgG prevalence of measles and rubella was higher than those herd immunity thresholds required to eliminate both viruses. However, the prevalence for antibodies for both pathogens in people aged 1-2 years was lower than herd immunity, indicating a need for a more robust immunization program. Special attention should be paid to the rubella vaccinations in 25-34 year olds to minimize the potential risk of creating congenital rubella syndrome.
