- A single dose of a commercial trivalent influenza subunit vaccine (SV) and two whole virus vaccines (WVV) were compared in a randomized, placebo-controlled field trial of subjects under 23 years of age in the Israel Defence Forces. Sixty percent of SV recipients and 29% and 37% of WVV recipients showed no measurable response to the H 1 N 1 subtype (A/USSR). When the prevaccination titer to H 1 N 1 was< 10, SV did not differ significantly from the placebo, and when⩾ 10, the SV was poorer than the WVV. Response to the H 3 N 2 (A/Texas) component was excellent, but when the prevaccination titer was< 10, SV appeared less immunogenic than WVV. All three vaccines performed equally against the B/Hong Kong strain.