Flu vaccine works in HIV-positive individuals

Influenza vaccine is effective in HIV-positive patients, according to the results of a large prospective Japanese study published in the June 1^st edition of the Journal of Acquired Immune Deficiency Syndromes. The investigators also found that CD4 cell count predicted the effectiveness of influenza vaccination in patients who did not have antibodies to influenza before vaccination.

Vaccination against influenza is recommended for HIV-positive individuals. “Influenza virus infection may be more prolonged in individuals with immune deficiency and can cause a transient increase in HIV-q viral load that might become relevant to the clinical course of HIV-1 infection”, write the investigators.

There have, however, been few studies looking at the protective effect of influenza vaccine in HIV-positive patients. These studies did not consider the effect of HIV viral load or the impact of HAART on immune restoration or on the efficacy of influenza vaccination.

Japanese investigators therefore wished to determine the clinical efficacy of influenza vaccination and to correlate it with immune response to the vaccine determined by increased antibody levels and anti-influenza specific CD4 T -cells.

Between November and December 2002, patients attending a large HIV outpatient clinic were offered influenza vaccination. The investigators restricted their analysis to a random selection of 262 individuals who accepted the vaccination and 66 patients who declined it.

Blood samples were obtained at the time of vaccination and then after eight and/or 16 weeks to determine immunological response to the vaccine, CD4 cell count and HIV viral load.

A total of 30 cases of influenza occurred in the study population, 16 cases in patients who received the vaccine (6%) and 14 cases in individuals who declined vaccination (21%). This difference was statistically significant (p

CD4 cell count was a factor in the risk of developing influenza. Amongst patients with a CD4 cell count above 200 cells/mm³ the incidence of influenza was 6% in vaccinated patients and 21% in unvaccinated patients. Once again, this difference was statistically significant (p 3.

The investigators then looked at the incidence of influenza in patients according to the use of HAART. They found that 6% of vaccinated individuals taking HAART developed influenza compared to 21% of unvaccinated patients taking HAART (p

In multivariate analysis, the investigators identified CD4 cell count (p

Influenza antibody titers were tested at weeks eight and/or 16 after vaccination. In patients who did not have antibodies to influenza at baseline, antibody response after vaccination was significantly affected by whether an individual had a CD4 cell count above or below 200 cells/mm³ (p

Amongst patients who had influenza antibodies at baseline, the response to the vaccination was not affected by whether a patient had a CD4 cell count above or below 200 cells/mm³.

The investigators then looked at influenza specific CD4 T-cell responses. They found that this response was affected by HIV viral load (p

The investigators conclude “our prospective study in a large population demonstrated that influenza vaccine provides protection of HIV-1 infected patients…annual vaccination of HIV-1 infected patients is thus recommended.”