Vaccines were urgently needed in 2009 against A/H1N1 pandemic influenza. Based on the H5N1 experience, it was originally thought that 2 doses of an adjuvanted vaccine were needed for adequate immunogenicity. We tested H1N1 vaccines with or without AF03, a squalene-based adjuvant, in children.
Two randomized, open-label, trials were conducted. Participants 3–17 y received two injections of 3.8 µg or 7.5 µg hemagglutinin (HA) with adjuvant or 15 µg HA without adjuvant. Participants aged 6–35 mo received two injections of 1.9 µg or 3.8 µg HA with full or half dose adjuvant or 7.5 µg HA without adjuvant.
All subjects 3 to 17 y reached seroprotection (hemagglutination inhibition (HI) titer ≥ 40) after the first dose of the adjuvanted vaccine, and 94% and 98% in the 3–8 and 9–17 y groups respectively with the non-adjuvanted vaccine. In children aged 6–35 mo responses were modest after one dose, but after two doses virtually all children were seroprotected regardless of HA or adjuvant dose. In this age group, antibody titers were 5 to 7 times higher after adjuvanted than non-adjuvanted vaccine. The higher responses with the adjuvanted vaccine were also reflected as better antibody persistence. There was no clustering of adverse events that would be suggestive of a safety signal.
While a single injection was sufficient in subjects from 3 y, in children aged 6–35 mo two injections of this A/H1N1 pandemic influenza vaccine were required. Formulation of this vaccine with adjuvant provided a significant advantage for immunogenicity in the latter age group.Full Text Options