Table 4.
Hemagglutination inhibition antibody of infants with antibody titer <1:10 pre‐vaccination against H1N1 influenza virus 21 days after the first and second injections of H1N1 vaccine or seasonal influenza vaccine
| Age and vaccine group | ||||||
|---|---|---|---|---|---|---|
| 6–23 months | 24–35 months | |||||
| 7·5 μg HA n = 57 | 15 μg HA n = 48 | Control n = 25 | 7·5 μg HA n = 52 | 15 μg HA n = 53 | Control n = 23 | |
| Pre‐vaccination | ||||||
| GMT (95% CI) | 5·00 (5·00–5·00) | 5·00 (5·00–5·00) | 5·00 (5·00–5·00) | 5·00 (5·00–5·00) | 5·00 (5·00–5·00) | 5·00 (5·00–5·00) |
| First injection | ||||||
| Seroprotection D21, N (%) | 26 (45·6) | 25 (52·1) | 5 (20·0) | 26 (50·0) | 31 (58·5) | 1 (4·3) |
| Seroconversion D21/D0, N (%) | 26 (45·6) | 25 (52·1) | 5 (20·0) | 26 (50·0) | 31 (58·5) | 1 (4·3) |
| GMT (95% CI) | 29·16 (20·44–41·62) | 31·75 (22·52–44·77) | 13·20 (8·58–20·31) | 31·47 (24·60–40·26) | 34·19 (27·44–42·59) | 7·40 (5·71–9·59) |
| GMTR D21/D0 (95% CI) | 5·83 (4·09–8·32) | 6·35 (4·50–8·95) | 2·64 (1·72–4·06) | 6·29 (4·92–8·05) | 6·84 (5·49–8·52) | 1·48 (1·14–1·92) |
| Second injection | ||||||
| Seroprotection D42, N (%) | 52 (91·2) | 47 (97·9) | 11 (44·0) | 48 (92·3) | 49 (92·4) | 4 (17·4) |
| Seroconversion D42/D0, N (%) | 52 (91·2) | 47 (97·9) | 11 (44·0) | 48 (92·3) | 49 (92·4) | 4 (17·4) |
| GMT (95% CI) | 163·94 (113·37–237·06) | 226·27 (168·51–303·83) | 32·04 (20·71–49·57) | 136·35 (100·64–184·72) | 153·84 (111·96–211·39) | 15·25 (10·16–22·90) |
| GMTR D21/D0 (95% CI) | 32·79 (22·68–47·42) | 45·26 (33·71–60·78) | 6·41 (4·14–9·92) | 27·27 (20·13–36·95) | 30·77 (22·39–42·28) | 3·05 (2·03–4·58) |
Seroprotection: number and proportion (%) with titers ≥40; seroconversion: number and proportion (%) with either a Day 0 titer <10 and a Day 21 titer ≥40, or a Day 0 titer ≥10 and ≥4‐fold rise by Day 21.
GMT, geometric mean titer; GMTR, geometric mean of post‐/pre‐vaccination titer ratio; N, number of participants; CI, confidence interval; D, day; HA, hemagglutinin.