Dynamics of neutralizing antibody titers at different time points after immunization with enterovirus type 71 vaccin

Abstract

Objective To observe the dynamics of neutralizing antibody titers at different time points after immunization with enterovirus type 71 (EV71) vaccine. Methods A randomized, open-label clinical trial was conducted. One hundred and twenty infants aged 6-35 months in Zhejiang province were recruited as subjects and were randomly divided into 3 groups. The serum was collected at 10 days, 20 days, and 30 days after 1 dose of EV71 vaccine in each group. EV71 neutralizing antibody was detected to study immunogenicity at different time points after initial immunization with EV71 vaccine. An open-label design was conducted to study 343 subjects in phase III clinical trials in Jiangsu province in 2012. Venous blood samples were collected to detect EV71 neutralizing antibodies 64 months after the first dose of vaccine was administered, so as to evaluate the antibody persistence over 5 years. Results The results of the Zhejiang study showed that the seropositive rate before inoculation was only 3.8%(4/104). Pre-immune antibody geometric mean titer (GMT) was 1:5.0. The seropositive rates of EV71 vaccine antibody at day 10, 20 and 30 after inoculation with 1 dose of EV71 reached 89.2% (33/37), 80.6% (25/31) and 66.7% (24/36), respectively and the GMTs were 1:24.6, 1:1:12.9, and 1:13.8, respectively. The seropositive rates (P<0.01) and GMT (Z10=-5.03, Z20=-3.73, Z30=-4.31, all P<0.01) at each time point were statistically higher than those before vaccination; The results of the Jiangsu study showed that the seropositive rates were 94.3% (100/106) and 71.4% (75/105) at 64-month in vaccine group and placebo group, respectively. The indicator was statistically higher in the vaccine group than that in the placebo group (x2=19.567, P<0.01). The GMT was 1:141.4 and 1:71.8, respectively and the indicator was statistically higher in the vaccine group than in the placebo group (t=2.60, P=0.01). Conclusions EV71 vaccine can stimulate immune response quickly after vaccination and showed good persistence over five years. Key words: Hand, foot, and mouth disease; Enterovirus infections; Viral vaccines; Immunocompetence