Potential for single high-dose influenza immunization in unprimed children.

High concentrations of split-product vaccine (SPV) are more immunogenic than lower concentrations. These studies were verified with another influenza strain, B/Singapore/22/79. Two ether-treated SPVs were compared in 80 children and young adults. The vaccine strains were influenza A/Bangkok/79, A/Brazil/78, and B/Singapore/79; 44 patients received a high-dose SPV containing 7, 7 and 60 micrograms each of the respective hemagglutinins (HA) and 36 received a standard dose SPV containing 7, 7, and 7 micrograms of HA, respectively. Among persons initially seronegative by hemagglutination inhibition (HAI) tests, the geometric mean titer (GMT) in 15 recipients of one high dose was 97 vs GMT of 37 in 18 recipients of one standard dose (P less than .05). Furthermore, 87% of high-dose recipients had HAI titer greater than or equal to 40 vs 44% of standard dose recipients. In initially seropositive persons, GMT in 29 recipients of one high dose was 170 vs GMT of 84 in 18 recipients of one standard dose (P less than .05). Immune response to the other two virus strains was comparable for the two vaccines. The reaction index for the high dose vaccine was 0.70 vs 0.45 for the standard dose (P = NS). An A/Bangkok epidemic struck the New York metropolitan area. The attack rate in unvaccinated matched sibling control subjects was 35% (15/43). There were no vaccine failures. In conclusions, in the small number of patients studied, a 60-micrograms HA dose of B/Singapore/79 was significantly more immunogenic than a standard 7-micrograms HA dose without an increase in reactogenicity.