Antibody levels to hepatitis B vaccine in underfive children vaccinated using dpt-hb vaccine in Dar es salaam, Tanzania.

Abstract

Background: Expanded Programme on Immunization (EPI) in Tanzania has been in existence since 1975. Its goal is to reduce infant and childhood morbidity and mortality due to vaccine preventable diseases. In 1991, The World Health Organization (WHO) called for all children to receive the hepatitis B vaccine. Since then 116 countries have added this vaccine to their routine immunization programme and the remaining countries are either planning its introduction or studying its feasibility. In Tanzania, Hepatitis B vaccination was introduced into immunization programme in 2002 and it is given in combination with DPT as DPT-HB (Diphtheria, Pertussis, Tetanus and Hepatitis B) at 4th, 8th and 1 th week of life. Objective: To determine immunity to Hepatitis B vaccine in children aged 2-59 months, vaccinated using DPT-HB vaccine attending reproductive and child health (RCH) clinics in Dar es Salaam, Tanzania. Methodology: Study design: A cross-sectional health facility based study was done. Settings: Reproductive and child health (RCH) clinics at Terneke, Amana and Mwananyamala Municipal hospitals in Dar es Salaam, Tanzania. Study population: Children less than five years of age who had received DPT-HB vaccine at 4th, s" and 1 z" week of life, according to Tanzania guidelines as evidenced on reproductive and child health (RCH) card no 1. Laboratory investigations: Blood samples were separated to obtain sera for anti-Hb.Ag, anti-Hls.Ag, HBsAg and HIV ELISA, and peripheral blood mononuclear cells for HIV DNA PCR for children less than 18 months of age. Anti-Hls, antibody levels 2:10 mIU/ml was regarded as protective. Results: Two hundred and ninety SiX children vaccinated with DPT-HB vaccme of whom, 153 (51.7%) were males and 143 (48.3%) females participated in the study. Overall 69.3%had antibodies within protective ranges. Age had significant correlation with anti-Hfs, antibody levels. Children below 36 months had higher antibody levels compared to children above 36 months of age (p=O.OlO). The proportion of children with adequate anti-Hfl, antibody levels was found to decrease with increasing time interval since last DPT-HB dose. (p=0.0089) Of 279 children who had completed 3 doses of Hepatitis B vaccine, 71 % had anti-Hjj, antibody levels ~l 0 mIU/mL. There was a statistical significant correlation between anti-Hfs, antibody levels and number of DPT- HB doses received (p<O.OOl). Children who were severely wasted did not mount adequate anti-Hll, antibody levels compared to well nourished children (p=O.OOl). Thirty one children (10.5%) were HIV positive, only 25.7% of them had protective anti-Hfs, antibody levels. Five children (1.7%) were found to be HBsAg positive suggesting possible vertical transmission because all of the studied children were anti-Hll.Ag negative. In multiple regression analyses, number of DPT-HB doses, HIV serostatus, and interval since last DPT -HB dose were significant predictors for the variation of anti-Hls, antibody levels after adjusting for the confounders; i.e. age and sex Conclusion: Well nourished, HIV uninfected children who completed the 3 DPT-HB vaccine doses had adequate anti-Hls, antibody levels. Recommendation: Children should complete three DPT-HB doses in order to mount adequate anti-Hls, antibody levels. There is a need of introducing hepatitis B vaccine booster at nine months of age along with measles vaccine. Good nutritional status to children and prevention of mother to child transmission (PMTCT) of HIV should continue to receive high priority to enable children mount adequate anti-Hls, antibody levels.