The immunogenicity of a novel A (H1N1) vaccine in HIV-infected children.

BACKGROUND: In October 2009, the United Kingdom Department of Health recommended vaccination of high-risk groups, including children with HIV, with a novel, oil-in-water AS03(B) adjuvanted Influenza A (H1N1) vaccine (Pandemrix). There were no published data available regarding the immunogenicity of this vaccine in such children. OBJECTIVES: This study evaluated the immunogenicity of the adjuvanted Influenza A (H1N1) vaccine in HIV-infected children immunised according to national recommendations and assessed the impact of vaccination on individual CD4 counts and HIV viral loads. METHODS: HIV-infected children attending outpatient appointments between 01 November and 31 December 2009 were offered two doses of H1N1 vaccine three weeks apart and a blood test before and 3 weeks after the second dose of vaccine. Serum antibody responses were determined by a haemagglutination inhibition (HAI) assay using standard methods. RESULTS: Of the 39 children recruited for vaccination, 31 (median age 11.2, range 3.0-17.9 years) received both doses of vaccine and provided pre- and post-vaccination blood samples. Eight children (26%) had baseline HAI titres ≥ 1:32. After vaccination, 29 children (94%, 95% CI, 78.6-99.2%) had HAI titres ≥ 1:32 (seroprotection), of whom 27 (87.1%, 95% CI, 70.1-96.4%) had also had a four-fold rise in titres (seroconversion). In the univariate analysis, post-vaccination geometric mean titres (GMTs) were higher among the 21 children receiving highly active anti-retroviral therapy compared with the 10 treatment-naïve children (GMT 406 [95% CI 218-757] vs. 128 [49-336]; P=0.035), but this was no longer statistically significant when adjusted for prevaccine GMTs. There was no significant impact of vaccination on CD4+ T cell count or HIV viral load. CONCLUSION: The AS03(B)-adjuvanted pandemic Influenza A (H1N1) vaccine is highly immunogenic and appears to be safe in HIV-infected children.