Antibody responses against vaccine-preventable infectious diseases in HIV-exposed and unexposed Malawian infants

Background The evaluation of immunological status with respect to vaccine-preventable infectious diseases allows to identify populations with suboptimal protection. HIV-exposed infants, even if not infected with HIV, have higher morbidity and mortality in comparison to their unexposed counterparts, and even if the underlying mechanisms have not been clearly elucidated, dysfunctional immune responses might be involved. The aim of this study was to evaluate post-vaccination immune responses in two groups of infants (HIV-exposed and HIV-unexposed) living in the area of Blantyre, Malawi, measuring IgG levels against Haemophilus Influenzae type B (HiB), Hepatitis B (HBV), and Streptococcus pneumoniae (PCP). Methods Sixty-two infants, 49 HIV-exposed, uninfected (HEU), born to women living with HIV, and 13 HIV-unexposed, uninfected (HUU), born to HIV-negative mothers, were included in the study. The infants were visited monthly, from birth to 12 months, and blood samples were collected at 6 months. Anti-HiB, -HBV and -PCP vaccines are administered in Malawi at 6, 10, and 14 weeks of life. The antibody responses to the vaccines were determined by ELISA tests. Results The geometric mean concentrations (GMCs) of anti-HiB, anti-HBs and anti-PCP antibodies were not different between the two groups. The proportion of infants with protective levels (> 0.15 mg/l) versus HiB was lower (although not significantly) in HEU in comparison to HUU infants (81.6% vs 100%, p = 0.095). There was no significant difference between the two groups in the proportion of infants with protective antibody levels against HBV or PCP, although this proportion was lower than expected in both groups, varying from 81.6–84%. Overall, only 61.3% of the infants showed protective levels against all three vaccine antigens. Conclusions The humoral response after vaccination was similar in HEU and HUU infants. A disturbingly high proportion of infants without protective antibody levels against HBV and PCP in both groups of infants and against HiB in HEU infants was observed.