Low levels of pertussis- and measles-specific IgG antibodies in 6-week-old HIV-exposed and -unexposed Malawian infants: implications for vaccination strategies and role of long term HIV therapy

Serological studies in infants can provide valuable information on the degree of protection conferred by IgG maternal passive transfer during early life. If infant levels are inadequate, protection may be incomplete, increasing the risk of life-threatening diseases such as pertussis and measles, before immunization completion. In addition, HIV infection, -highly prevalent in African countries like Malawi-may impair transplacental antibody transfer. We determined anti-Pertussis Toxin (PT) and anti-measles IgG in 86 6-week-old infants, born to mothers living with HIV (HIV-exposed uninfected, HEU, n = 58) and to HIV-negative mothers (HIV-unexposed uninfected, HUU, n = 28). The HEU group was divided into two subgroups: Infants born to mothers who initiated antiretroviral therapy (ART) during pregnancy (Short-ART, SA-HEU group, n = 29) or already in stable ART (Long-term ART, LA-HEU group, n = 29). The mean anti-PT and anti-measles IgG levels (1.97 IU/ml and 32.9 mIU/ml, respectively) were comparable between the HUU and HEU infants. Overall, only 12.8% and 18.6% of all infants had IgG levels above the protective thresholds for pertussis and measles, respectively. The duration of ART significantly influenced the infant's serological profile, with SA-HEU infants showing significantly lower IgG levels compared to both HUU and LA-HEU infants. Protecting infants during early life remains a significant health challenge in many middle and low-income countries. Achieving better early serological protection requires the implementation of diverse vaccination strategies. This study emphasizes the crucial importance for women living with HIV to be on stable ART before pregnancy.