Immune response and associated factors to Hepatitis B vaccination among children under five attending care at the Mulago Hospital Assessment Centre Paediatrics Clinic

Abstract

Background: Hepatitis B Virus vaccination is the cornerstone of prevention of the HBV infection especially in at-risk groups like children under five that are 60- 90% more likely to seroconvert to Chronic Hepatitis B infection unlike adults who are less < 5% likely to seroconvert. According to WHO, a proportion of 5–10% of infants have a poor response to vaccination, and will remain susceptible to HBV and its complications. The paucity of data on the Immune response to HBV vaccination among children raises the question of how protected are our children in Uganda are. Objective: To determine the immune response to Hepatitis B vaccination and associated factors among children under five attending the outpatient care at Mulago Assessment Centre (MAC) Pediatrics clinic. Methods: This was a cross-sectional study among children 1 to < 5 years attending MAC Paediatrics clinic at Mulago National Referral Hospital who met the eligibility criteria in the month of February, 2023. All children 1-5 whose caregivers gave consent were enrolled and a pretested study questionnaire was administered by trained research assistants. Blood samples were taken for analysis; Hepatitis B core antibody screening and anti HBs Ag titres by Electrochemiluminescence using the Cobas 6000 chemistry machine. Descriptive analysis using proportions was used to determine prevalence of the immune response in the different categories i.e. Good response or Poor response. Logistic regression analysis was done to determine factors that were independently associated with the different categories of immune response. Results: The 301 children recruited had ages ranging between 1 and 4 years with the highest number,89/301 (29.6%), aged 2 years. All the children tested negative for the Hepatitis B core antibody screen. The immune response represented by the Hepatitis B antibody titers ranged from 2 IU/ml to 1000 IU/ml. The children had a median Hepatitis B antibody titer of 86.2 IU/ml (IQR: 14.5, 239.4). The prevalence of good immune response was 77.4% (233/301) (95% CI: 72.3% - 81.8%) and the proportion of very good responders was 58.4% (136/233)(136/233) (95% CI: 51.9% - 64.6%). The factors that were found to be significantly associated with a good immune response included: Child Age and caregiver HIV status. Children aged 3 years were 60% less likely to have a good response compared to children aged 1 year (aOR=0.40; 95% CI: 0.16 - 0.97; p=0.044). Children whose caregivers had an unknown HIV status were 83% less likely to have a good response compared to children whose caregivers had a known HIV status (aOR=0.17; 95% CI: 0.04 - 0.71; p=0.014). Conclusion: Children at MAC Paediatrics clinic had a protective level of antibodies to HBV vaccine at 77%; however, this is still below the expected level by WHO of at least 95%. Younger age and having a negative HIV status of the caregivers were independently found to be associated with a good immunological response to the vaccine. Emphasis needs to be made on the Hepatitis B birth dose vaccination recently rolled out and possibly a booster dose for children over 1 year especially those at risk. We also urge scholars to further study the immunological response to Hepatitis B vaccination among children.