Antibody responses to vaccines are suboptimal in immunosuppressed HIV-positive individuals. This study aimed to evaluate the potential benefits of MF59® adjuvant or a second A/H1N1 influenza vaccine dose in HIV-positive adults.

HIV-positive adults (n = 61) and HIV-negative controls (n = 93) aged 18–60 years received two doses of A/H1N1, either as MF59-adjuvanted A/H1N1 pandemic vaccine, or as part of a unadjuvanted seasonal influenza vaccine containing the pandemic strain. Immunogenicity was assessed against the vaccine strain, A/California/7/2009, by haemagglutination inhibition (HI) assay three weeks after the administration of each vaccine dose. Local and systemic reactions were recorded for three days after each vaccination. Unsolicited adverse events were recorded throughout the six-week study period.

Both adjuvanted and unadjuvanted vaccines met the European licensure criteria in HIV-positive and HIV-negative study groups after a single dose. Lower antibody titres were observed with both adjuvanted and unadjuvanted vaccine in HIV-positive compared to HIV-negative subjects. A second dose of either vaccine did not compensate for the lower response of HIV-infected subjects. In HIV-positive subjects, CD4⁺ T cell counts and levels of CD38 expression on CD8⁺ T cells remained stable throughout the study period. Both vaccine formulations were generally well tolerated, with no increased reactogenicity observed in response to the adjuvanted vaccine.

Antibody responses in HIV-positive subjects were acceptable but lower than those in healthy control subjects, whether subjects were immunized with one or two doses of adjuvanted or unadjuvanted vaccine. Vaccination did not affect rates of HIV replication, CD4⁺ T cells counts, or levels of CD38 expression among patients under successful antiretroviral treatment.