The status of protective measles antibodies in HIV-1 positive and negative infants aged 6 and 9 months in urban Lusaka,Zambia

Abstract

BACKGROUND – Measles remains the leading cause of vaccine preventable disease that contributes to under 5 mortality rate despite the availability of a safe and effective vaccine. During the 2010-2011 measles outbreak, infants aged 0-8 months constituted 39% of the total population of children admitted with measles infection at UTH in Lusaka, Zambia. None of these infants were vaccinated against measles because they were below the age of vaccination of 9 months. The optimal time for measles vaccination in infants has not been revised since the vaccine was introduced in 1966. The age at which passively acquired maternal measles antibodies decay is critical in determining the optimal age for measles vaccination in infants, particularly in HIV exposed infants who may have acquired low maternal antibodies, and even in those who are not HIV exposed. RESEARCH DESIGN AND METHODS – A cross-sectional study of 126 infants aged six and nine months old along with their respective mothers was carried out and participants were screened for measles antibodies in their oral fluid. The study was carried out at the under 5 clinics at Kanyama and Chilenje health centres in urban Lusaka, Zambia from October 2014 to December 2014. Demographic and clinical data were collected using a structured questionnaire. Measles antibodies were measured in the oral fluids of the mothers and infants using the enzyme-linked immunosorbent assay (ELISA) test. RESULTS – One hundred and one (81.4%) of the infants included in the study had no protective maternal measles antibodies in their oral fluids. Eighty three percent (83%) of the 6 months and 93% of the 9 months old infants had unprotective measles IgG antibodies detected. Twenty eight (22%) of the infants included in the study were exposed to HIV. Four (14.2%) of the HIV exposed and 8 (8.1%) of the HIV non exposed infants had protective measles antibodies. Only 87 (69%) of the mothers had positive measles IgG antibodies. None of the study variables had significant influence on the status of maternal measles antibodies in the infants - maternal and infant HIV status, infant birth weight, prematurity, maternal measles IgG antibody status as well as maternal and infant nutritional status. CONCLUSION – The findings in this study suggest that 81.4% of the infants in the studied population are susceptible to measles infection before the age of immunization at 9 months. A lot of other studies done in different regions of the world have demonstrated early loss of maternal measles antibodies below the age of vaccination and have recommended early immunization in infants to reduce susceptibility to measles infection. This study calls for more large scale studies to determine the appropriate age for measles vaccination in the Zambian infant population.