HI antibody response in volunteers vaccinated with live influenza A/New Jersey/76 vaccine

Live freeze-dried influenza A/New Jersey/76 vaccine prepared from the "cold-adapted variant" of NIB-3 strain. Three groups of about 50 persons were included in a double-blind placebo-controlled field trial. One group received the vaccine with 7 log EID50/dose, the other 6 log EID50/dose and the third received placebo. One half of persons from each group were given a second dose of the corresponding preparation after two weeks. The immunogenicity of the vaccine was evaluated by the determination of HI antibody conversion rate in seronegative persons. The proportion of vacinated persons with seroconversion, regardless of the number of doses, increased with time, and 16 weeks after vaccination reached the maximum value of 0.87 in persons given vaccine with 7 log EID50 per dose and 0.55 in those given 6 log EID50/dose. In twice-vaccinated persons the proportion of seroconversion was higher regardless of the virus titre of the vaccine. The highest proportion of seroconversion (0.93) was recorded in persons vaccinated twice with 7 log EID50/dose 16 weeks after vaccination.