Influenza Vaccination of HIV Infected Pregnant Women: Safety and Immunogenicity (MatfluHIVpos)

Determining the contribution of influenza to early childhood morbidity and mortality in sub-Saharan Africa and the potential to prevent influenza disease through vaccination may contribute to reducing childhood deaths; since influenza illness is a vaccine preventable disease for which vaccines are developed, licensed and available at reasonable cost. Unfortunately, infants at highest risk for serious disease are those under 6 months of age, for whom trivalent inactivated influenza vaccine (TIV) is poorly immunogenic and not licensed. As pregnant women also have an increased risk of serious illness (3.3-5.5 fold for hospitalization for influenza-associated acute cardio-respiratory illness) from influenza infection, one strategy to prevent the complications of influenza in pregnant women and young infants is through maternal TIV immunization, which is recommended by the WHO. This could result in direct protection of the women and protection of the young infant consequent to transplacental transfer of TIV induced antibody.

Barriers to administration of vaccines during pregnancy including lack of information on effectiveness and concerns about safety probably explain the virtual non-existent use of TIV in pregnant women from low-middle income countries, including South Africa.

The immunogenicity and efficacy of TIV in HIV-infected adults was only recently documented in an African setting. A placebo-controlled, community-based randomized, placebo controlled trial, conducted in South Africa reported that TIV was associated with a 75% reduction in influenza-confirmed illness. The results of the study also confirmed the safety of TIV among African HIV-infected adults. The study, however, only included 7 women who were pregnant. In addition to no differences in solicited adverse event rates, there was also no difference in either CD4+ cell count changes or HIV viral control in those on antiretroviral treatment between TIV vaccinees compared to placebo recipients. This allayed previous concerns regarding the potential negative effect of TIV which centered around the observed transient increase in HIV-1 viral load, even in HIV infected individuals on ART and who were virologically suppressed (viral load <400 copies/ml). Decreases in CD4+ lymphocyte counts have also been observed in HIV-infected individuals post TIV vaccination. These changes, however, even in past studies were infrequent (4-18%) and resolved at later time-points and were considered to be clinically non-significant.

Only recently has data become available from Bangladesh in which the benefit of maternal TIV vaccination was demonstrated by a 63% (95%CI 5 to 85) reduction in laboratory-confirmed influenza illness in infants under 24 weeks of age in children born to mothers vaccinated with TIV and a 36% reduction in clinical illness in vaccinated mothers. There has, however, not been any study on the effectiveness of maternal immunization with TIV on influenza- associated morbidity and mortality either in the mothers or infants in African settings.

Despite the encouraging results on maternal immunization from Bangladesh, and the preliminary data supporting that TIV is efficacious mainly in HIV-infected non-pregnant adults, further data are needed to advocate for routine use of TIV during pregnancy in settings with a high prevalence of HIV. Reasons for this include that the impact of maternal HIV on the kinetics of TIV induced transplacental antibody transfer cannot be derived from available data. This is important as the primary focus of this proposal, and major potential public health benefit of maternal TIV vaccination, is targeted at protection of young infants. HIV infection is known to decrease placental integrity and lower antibody levels in the fetus and newborn. Furthermore, maternal hypergamma-globulinemia that is characteristic of HIV-infection may be associated with decreased neonatal antibody levels. This paradox is explained by the limited number of placental antibody receptors, resulting in IgG antibodies competing for available receptors and thereby decreasing vaccine-specific antibody transport. Preterm birth increases with HIV, chronic maternal disease or malnutrition. Transfer of maternal antibody which is gestational age dependant, may be more affected by maternal immunization in sub-Saharan Africa where these conditions are common.

The overall aim of this project is to evaluate the safety and immunogenicity of TIV vaccination of HIV-infected pregnant women