Protective effect of single-dose adjuvanted pandemic influenza vaccine in children

Background During the first wave of A/California/7/2009(H1N1) influenza, high rates of hospitalization in children under 5 years were seen in many countries. Subsequent policies for vaccinating children varied in both type of vaccine and number of doses. In Canada, children 36 months to < 10 years received a single dose of 0 center dot 25 ml of the GSK adjuvanted vaccine (Arepanrix (TM)) equivalent to 1 center dot 9 mu g HA. Children 6 months to 35 months received two doses as did those 36-119 months with chronic medical conditions. Method We conducted a community-based case-control vaccine effectiveness (VE) review of children under 10 years with influenza like illness who were tested for H1N1 infection at the central provincial laboratory. Laboratory-confirmed influenza was the primary outcome, and vaccination status the primary exposure to assess VE after a single 0 center dot 25-ml dose. Results If vaccination was designated to be effective after 14 days, no vaccinated child had laboratory-confirmed influenza compared to 38% of controls. The VE of 100% was statistically significant for children < 10 years of age and < 5 years considered separately. If vaccination was considered effective after 10 days, VE dropped to 96% overall but was statistically significant and over 90% in all age subgroups, including those under 36 months. Conclusions A single 0 center dot 25-ml dose of the GSK adjuvanted vaccine (Arepanrix (TM)) protects children against laboratory-confirmed pandemic influenza potentially avoiding any increased reactogenicity associated with second doses. Adjuvanted vaccines offer hope for improved seasonal vaccines in the future.