CTN 253: H1N1 flu vaccine study in HIV-positive adults

About The Study

This study evaluated the safety and immune response of the pandemic H1N1 (2009) influenza vaccine in HIV-positive adults. Researchers assessed and compared which dosing level was best able to produce an optimal immune response to the vaccine. Researchers were looking to see if a booster dose of vaccine would increase the protection obtained by the vaccination.

Study Approach

A phase III, randomized trial was conducted at four Canadian sites. Two dosing strategies (standard dose vs standard dose plus booster on day 21) were assessed in HIV-positive participants aged 20 to 59 years during the H1N1 (2009) pandemic. A single antigen, inactivated split adjuvanted (AS03(A)) influenza vaccine (Arepanrix) was used. A test to determine the amount of the antigen in the blood serum was done at days 21 and 42 and at month 6.

Study Population

HIV-positive individuals aged 20 to 59 years at four Canadian sites (Ottawa, Toronto, Montreal, Halifax).

Results

One hundred and fifty participants received at least one injection. Within the two study arms both groups had similar baseline parameters: 83 per cent male, 85 per cent on HAART, median CD4 was equal to 519 cells/mm(3), 84 per cent with HIV RNA less than 50 copies/mL. At day 21, Seroprotection, the protection achieved by the vaccination was achieved in 80 per cent (95 per cent CI, 70-89) of participants. Seroconversion, the development of specific antibodies in the blood serum occurred in 74 per cent of participants (63-85). Seroprotection and seroconversion were further improved in those randomized to booster dosing: at day 42, 94 per cent (85-98) versus 73 per cent (60-83) (P < .01) and 86 per cent (75-93) versus 66 per cent (5-77) (P = .01). Seroprotection was retained in 40 per cent (28-54) of recipients at month six with trends toward greater retention of immunity in booster recipients. A smaller sub-study (64 participants) found that two doses of the vaccine is better at producing long-term (6 month) protection.

Conclusion

High-level immune response was achieved with a single dose of the vaccine. Immune response was further improved with booster dosing. Use of this vaccine and booster represent an important approach to increasing immune response in a population that has a diminished degree of responsiveness to vaccines. A two-dose immunization strategy may provide superior long-term protection for people living with HIV.