Abstract
BackgroundWe previously reported that despite HIV-infected pregnant women had modest humoral immune responses to inactivated influenza vaccine (IIV) measured by hemagglutination-inhibition (HAI) assay, the observed vaccine efficacy against influenza disease was higher than predicted by HAI; suggesting that IIV may confer protection to HIV-infected individuals by additional mechanisms. We evaluated the response to IIV by microneutralization (MN) and HAI assays and correlated both methods in HIV-infected and HIV-uninfected pregnant women.MethodsMN and HAI antibodies were measured pre-vaccination and approximately one-month post-vaccination in 80 HIV-infected and 75 HIV-uninfected women who received IIV. Geometric mean titers (GMTs), fold-change in titers and seroconversion rates were determined for the three influenza stains in the vaccine.ResultsAfter vaccination there were significant increases in MN and HAI GMTs for the three vaccine strains in both HIV-infected and HIV-uninfected women. HIV-infected women had, however, a lower immune response compared to HIV-uninfected. Fold-increases were 2 to 3-times higher for MN assay compared to HAI assay for the influenza-A strains. Also a higher percentage of women seroconverted by MN than by HAI assay for the influenza-A strains. There was high positive correlation between MN and HAI assays, except for the B/Victoria strain at pre-vaccination.ConclusionsIn general, the MN assay was more sensitive than the HAI assay. Microneutralization antibodies might correlate better with protection against influenza infection.
Highlights
Annual influenza vaccination is recommended for groups at high-risk for severe influenza infections, including pregnant women and HIV-infected individuals [1]
A higher percentage of women seroconverted by MN than by HAI assay for the influenza-A strains
In a placebo-randomized clinical trial we reported that immunization of HIV-uninfected and HIV-infected pregnant women with seasonal trivalent inactivated influenza vaccine (IIV) was safe, immunogenic and partially protected the vaccinated women against polymerase chain reaction (PCR)confirmed influenza-illness [2]
Summary
Annual influenza vaccination is recommended for groups at high-risk for severe influenza infections, including pregnant women and HIV-infected individuals [1]. The lower HAI response in HIV-infected women did not, translate into inferior vaccine efficacy against PCR-confirmed influenza compared to HIV-uninfected women (57.7% vs 50.4%, respectively) [2, 3] These data indicate that IIV may confer protection to HIV-infected individuals by mechanisms other than HAI antibodies. The HAI assay is the most commonly used methodology to determine responses following influenza vaccination because of its relative correlation with protection, as well as its ease of performance, good standardization between laboratories and low price [4] This assay detects antibodies to the viral surface protein hemagglutinin (HA) that can prevent agglutination to sialic-acid residues on erythrocytes, HAI titers only measure antibodies that block receptor binding of the virus to host cells, and it is only a correlate of the capacity of antibodies to inhibit viral infection of host cells in the respiratory tract [5]. We evaluated the response to IIV by microneutralization (MN) and HAI assays and correlated both methods in HIV-infected and HIV-uninfected pregnant women
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