Immune response after two doses of the novel split virion, adjuvanted pandemic H1N1 influenza A vaccine in HIV-1-infected patients.

Background: To determine the rate of seroconversion after 2 doses of a novel split virion, inactivated, adjuvanted pandemic H1N1 influenza vaccine (A/California/7/2009) in human immunodeficiency virus type 1 (HIV-1)-infected patients (ClinicalTrials.gov NCT01017172).

Methods: Diagnostic study of adult HIV-1-infected patients scheduled for H1N1 influenza A vaccination. Blood samples where taken before and 21 days after the first dose and 21 days after the second dose of the vaccine. Antibody (AB) titers were determined by hemagglutination inhibition assay. Seroconversion was defined by either an AB titer ≤ 1:10 before and ≥ 1:40 after or ≥ 1:10 before and a ≥ 4-fold increase in AB titer 21 days after vaccination.

Results: One hundred thirty-five patients received 2 doses of the H1N1 vaccine and were analyzed. The rate of seroconversion was 68.2% (95% confidence interval, 59.6-75.9) after the first dose and 91.9% (95% confidence interval, 85.9-95.9) after the second dose. Patients who did not seroconvert had a lower mean nadir CD4 cell count (± standard deviation; 81 ± 99 vs 190 ± 148 cells/μL; P = .006), had a longer duration of HIV infection (± standard deviation; 13.1 ± 5.9 vs 8.8 ± 6.8 years; P = .04), and were more likely to have an AB titer ≥ 1:40 before vaccination (4% vs 55%; P < .001) when compared with patients with seroconversion. No other differences were found between the 2 groups, including AIDS status, highly active antiretroviral therapy status, HIV RNA - polymerase chain reaction load <50 copies/mL, CD4 cell count, sex, body mass index, and chronic hepatitis.

Conclusion: Among HIV-infected patients, the rate of seroconversion after the first dose of an adjuvanted H1N1 influenza A vaccine was 68% and increased to 92% after a second doses.