Abstract:
BACKGROUND
There are limited data on the efficacy of vaccination against confirmed influenza
in pregnant women with and those without human immunodeficiency virus (HIV)
infection and protection of their infants.
METHODS
We conducted two double-blind, randomized, placebo-controlled trials of trivalent
inactivated influenza vaccine (IIV3) in South Africa during 2011 in pregnant women
infected with HIV and during 2011 and 2012 in pregnant women who were not
infected. The immunogenicity, safety, and efficacy of IIV3 in pregnant women and
their infants were evaluated until 24 weeks after birth. Immune responses were
measured with a hemagglutination inhibition (HAI) assay, and influenza was diagnosed
by means of reverse-transcriptase–polymerase-chain-reaction (RT-PCR) assays
of respiratory samples.
RESULTS
The study cohorts included 2116 pregnant women who were not infected with HIV
and 194 pregnant women who were infected with HIV. At 1 month after vaccination,
seroconversion rates and the proportion of participants with HAI titers of
1:40 or more were higher among IIV3 recipients than among placebo recipients in
both cohorts. Newborns of IIV3 recipients also had higher HAI titers than newborns
of placebo recipients. The attack rate for RT-PCR–confirmed influenza among
both HIV-uninfected placebo recipients and their infants was 3.6%. The attack
rates among HIV-uninfected IIV3 recipients and their infants were 1.8% and 1.9%, respectively, and the respective vaccine-efficacy rates were 50.4% (95% confidence
interval [CI], 14.5 to 71.2) and 48.8% (95% CI, 11.6 to 70.4). Among HIV-infected
women, the attack rate for placebo recipients was 17.0% and the rate for IIV3 recipients
was 7.0%; the vaccine-efficacy rate for these IIV3 recipients was 57.7%
(95% CI, 0.2 to 82.1).
CONCLUSIONS
Influenza vaccine was immunogenic in HIV-uninfected and HIV-infected pregnant
women and provided partial protection against confirmed influenza in both groups
of women and in infants who were not exposed to HIV. (Funded by the Bill and
Melinda Gates Foundation and others; ClinicalTrials.gov numbers, NCT01306669
and NCT01306682.)
