Influenza vaccine effective in HIV-positive adults

A poster at IAS 2009 by Madhi and colleagues reported the results of a double-blind, randomised, placebo-controlled trial to examine the efficacy of influenza vaccines in HIV-positive adults. Specifically, the study tested the seasonal trivalent subunit vaccine, which protects against three H1N1 and H3N2 influenza strains, two of which were isolated in 2006 and one in 2007. [1]

This was the first community-based randomised controlled trial of the trivalent subunit influenza vaccination in HIV-positive adults. A previous randomised controlled trial in the US on HIV-positive out-patients at a military health facility found that 10/47 patients who received placebo acquired laboratory confirmed influenza versus 0/55 patients who received this type of vaccine (p<0.001). [2]

A Cochrane Review of the vaccine in healthy adults has found this type of vaccine to be 30% effective (95%CI 17%-41%) against influenza-like illness, and 80% (95% CI 56% to 91%) effective against influenza when the vaccine matched the circulating strain and circulation was high, but decreased to 50% (95%CI 27%-65%) when it did not match the circulating strains. [3]

Participants were vaccinated prior to the 2008 influenza season in South Africa. Oropharyngeal swabs were taken from patients with influenza-like symptoms or respiratory illness. Culture and PCR tests were used to identify influenza strains. Only events 14 days post-vaccination were compared.

The number of HIV-positive people enrolled was 506. Of these, 101 were ART-naive (52 received vaccine, 49 received placebo) and 405 were on ART (203 received vaccine, 202 received placebo). Median age was 36. Female to male ratio was 5 to 1 in the vaccine arm and 6 to 1 in the placebo one. Median CD4 was 372 (IQR: 254-489) and 363 (IQR: 252-517) in the two arms respectively. Nine women were pregnant in the vaccine arm and four in the placebo one.

Over 90% of patients on HAART were virally suppressed in both arms. The median time on HAART at the time of randomisation was 23 months.

The percentage of people who developed influenza on the placebo arm was 5.3% using a passive surveillance method. [4] The rate of influenza illness was 0.06 per 100 person weeks in the vaccine arm and 0.25 per 100 person weeks in the placebo one. The vaccine efficacy was 75.4% (95%CI 14-93). The protective effect against the seasonal H1N1 strain was 73.5% (95%CI 4-93). There was one case of influenza B and no cases of H3N2 or untyped A.

The authors concluded that their findings support the use of the trivalent subunit influenza vaccine in HIV-positive adults.

Comment

This study supports vaccinating HIV-positive adults against seasonal influenza, as is routinely recommended in the UK. Because the vaccine is developed seasonally, its efficacy will change from year to year. The seasonal vaccine does not provide protection against the current H1N1 strain of swine flu.

At present there is no data on the effect influenza vaccines would have on reducing mortality in HIV-positive people as the contribution of HIV to influenza mortality is not well understood. Nevertheless, it is plausible that the reduced influenza cases conferred by the vaccine will reduce mortality as well.