Comparison 15. 1968 to 1969 pandemic: inactivated polyvalent aerosol influenza vaccine versus placebo.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Influenza‐like illness	2	1000	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.46, 0.95]
1.1 Inactivated polyvalent aerosol vaccine versus placebo ‐ non‐matching ‐ 1 dose	2	644	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.32, 1.27]
1.2 Inactivated polyvalent aerosol vaccine versus placebo ‐ non‐matching ‐ 2 doses	1	356	Risk Ratio (M‐H, Random, 95% CI)	0.65 [0.44, 0.97]