Response to 2009 pandemic and seasonal influenza vaccines co-administered to HIV-infected and HIV-uninfected former drug users living in a rehabilitation community in Italy

Abstract

Background: 2009 A(H1N1) pandemic influenza vaccination was recommended as a priority to essential workers and high-risk individuals, including HIV-infected patients and people living in communities.

Methods: HIV-infected and HIV-uninfected former drug-users (18-60 years old) living in a rehabilitation community (San Patrignano, Italy) received one dose of a MF59-adjuvanted 2009 pandemic influenza vaccine and one dose of a 2009-2010 seasonal trivalent inactivated influenza vaccine (containing A/Brisbane/59/2007(H1N1), A/Brisbane/10/2007(H3N2), B/Brisbane/60/2008) simultaneously. Antibodies against each vaccine antigen were determined at the time of vaccination and one and six months post-vaccination by hemagglutination-inhibition test.

Results: 49 HIV-infected and 60 HIV-uninfected subjects completed the study. Most (98%) HIV-infected participants were on antiretroviral treatment, the median CD4+ cell count was 350 (IQR 300)cells/μl and viremia was suppressed in 91.8% of cases. One month post-vaccination, no significant changes in immune-virological parameters were observed. One month post-vaccination, the immune responses to both pandemic and seasonal vaccine met the EMA-CPMP criteria for immunogenicity of influenza vaccines in both HIV-infected and HIV-uninfected subjects. No difference in vaccine responses was observed between the two groups. Six months after vaccination, the percentages of vaccinees with antibody titres ≥1:40 and antibody geometric mean titres significantly decreased in both groups. However, they were significantly lower in HIV-infected than in HIV-uninfected vaccinees. In subjects who had been primed to seasonal influenza the year before (through either vaccination or natural infection), levels of antibodies against 2009 A(H1N1) were higher than those measured in unprimed subjects, both one month and six months post-vaccination.

Conclusions: The co-administration of a single dose of 2009 pandemic MF59-adjuvanted influenza vaccine with a seasonal vaccine provided a protective immune response in both HIV-infected and HIV-uninfected individuals. Subjects who had been primed to seasonal influenza in the year preceding the pandemic had a more vigorous and long-lasting antibody response to 2009 pandemic vaccine.