Results of the multiple-treatments meta-analysis comparing different influenza 2009 H1N1 formulations.

Only randomized trials were included.*Numbers refer to doses of Hemagglutinin antigen in micrograms. Risk differences (RD), with their respective 95% credible intervals (CI), compared with a vaccine including 1.88–5.25 µg hemagglutinin antigen and non-aluminum adjuvants (baseline comparator). RD expresses the absolute difference in risk between the two groups that is attributable to the intervention—i.e., if the likelihood of seroconversion in the reference group is 0.80 and it is 0.50 in the experimental group, the risk difference will be 0.80−0.50 = 0.30. The baseline value for hemagglutination–inhibition is 83.4% after the first or single dose; 96.5% after two doses. Aluminum adjuvants were aluminum hydroxide or aluminum phosphate. Non-aluminum adjuvants were oil-in-water emulsions.