Abstract

Introduction: Measles is an endemic but largely neglected disease in Lao People’s Democratic Republic. New-borns are protected by maternal antibodies, but antibody waning before measles vaccination at 9 months of age leaves infants susceptible to infection. In this study, the susceptibility window of infants was determined to generate scientific evidence to assess the national measles immunization strategy. Methods: Between 2015 and 2016, demographic data, medical history, and blood samples were collected from 508 mother-child pairs at the provincial hospital in Vientiane. The samples were screened with a commercial kit detecting anti-measles IgG antibodies. Results: The large majority (95.7%) of the mothers were seropositive for anti-measles IgG and antibody titers of the mothers and infants were highly correlated (p < 0.01). While at birth 97.7% of the infants were seropositive, seropositivity rates decreased to 74.2% two months later to reach only 28.2% four months after birth (p < 0.01). Just before the first dose of the measles-rubella vaccine, scheduled at 9 months of age, was actually given, less than 14% of the infants were seropositive. Conclusion: This alarmingly wide susceptibility gap due to rapid maternal antibody decay leaves infants at risk of measles infection and serious disease complications. A high herd immunity is crucial to protect young infants and can be achieved through improved routine vaccination coverage and (expanded age group) supplementary immunization activities.

Highlights

  • Measles is an endemic but largely neglected disease in Lao People’s Democratic Republic

  • Blood was collected by heel-prick on filter paper (Dried Blood Spots-dried blood spots (DBS)) from 378 infants without history of measles infection, who attended the paediatric unit for routine immunizations with the pentavalent vaccine recommended at weeks 6, 10, and 14 or MCV1 vaccination recommended at 9 months of age

  • Paired serum and DBS samples of eight anti-measles IgG positive volunteers were tested in triplicates and in parallel on two different ELISA plates

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Summary

Introduction

Measles is an endemic but largely neglected disease in Lao People’s Democratic Republic. New-borns are protected by maternal antibodies, but antibody waning before measles vaccination at 9 months of age leaves infants susceptible to infection. Results: The large majority (95.7%) of the mothers were seropositive for anti-measles IgG and antibody titers of the mothers and infants were highly correlated (p < 0.01). Just before the first dose of the measles-rubella vaccine, scheduled at 9 months of age, was given, less than 14% of the infants were seropositive. Conclusion: This alarmingly wide susceptibility gap due to rapid maternal antibody decay leaves infants at risk of measles infection and serious disease complications. Infants of measles-seropositive mothers are protected by maternal antibodies that were transmitted transplacentally to the foetus. Gestational age of the child, maternal nutrition, as well as maternal vaccination and infection status determine the level of antibodies passively acquired by the child and as a result the duration of post-natal protection [5,6]

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