Immune responses to measles and tetanus vaccines among Kenyan human immunodeficiency virus type 1 (HIV-1)-infected children pre- and post-highly active antiretroviral therapy and revaccination.

Ninety percent of the estimated 2.2 million children infected with human immunodeficiency virus type 1 (HIV-1) worldwide live in sub-Saharan Africa (UNAIDS). This population of children has increased morbidity and mortality, the causes of which are largely infectious in nature and often vaccine preventable. HIV-1-infected children have greater rates of diarrhea, pneumonia, and measles than HIV-1-uninfected children1–3, and increased severity of disease, particularly measles4–6. Many of the diseases affecting HIV-1-infected children are preventable with immunization, but HIV-1-infected children have decreased response rates to vaccines, including measles and tetanus4,7–9. Seroconversion rates of healthy, HIV-1 uninfected children for both measles and tetanus vaccine are greater than 90%10,11. In comparison, initial response rates to measles and tetanus vaccination among HIV-1-infected children are reported to range between 25%–88% and 60%–100%, respectively11–13. In addition to inadequate immune responses following vaccination, HIV-1-infected children may lose responses over time as they progress to AIDS. Measles and tetanus antibody responses post-vaccination have been shown to wane more rapidly among HIV-1-infected than uninfected children, with fewer than 50% maintaining protective levels 2 years after vaccine administration8,11,14. In non-African cohorts, HAART and re-vaccination appear to be successful strategies for boosting immunity against measles and tetanus15–17, but current WHO guidelines do not include repeat pediatric immunization following HAART12,18. Lack of effective measles and tetanus immunization strategies among HIV-1-infected children may result in a growing disease-susceptible population which could have important public health implications19. Half of all measles-related deaths and the majority of the world’s tetanus burden are in sub-Saharan Africa, the region with the highest HIV/AIDS burden20. Measles deaths account for up to 45% of all vaccine preventable deaths in Africa, and measles directly or indirectly accounts for 20% of child mortality among children younger than 5 years in Kenya21. In this study we determined immunity against measles and tetanus in a cohort of previously vaccinated HIV-1-infected Kenyan children before initiating HAART. We also assessed the impact of HAART on measles and tetanus IgG antibody responses before and after re-vaccination and defined correlates of immunity at baseline and during follow-up.