Table 2.
Immunogenicity after the first and second doses of the monovalent MF59-adjuvanted influenza virus H1N1 (2009) vaccine, as measured by a hemagglutination inhibition assay
| Immunogenicity endpoint | Value for: |
Total | P value | |
|---|---|---|---|---|
| Persons never or occasionally vaccinated with seasonal influenza virus vaccine | Persons always vaccinated with seasonal influenza virus vaccine | |||
| Baseline | ||||
| No. of persons | 443 | 54 | 498b | |
| Geometric mean titer | 5.8 | 7.2 | 5.9 | 0.019 |
| No. (%) of persons with HI titer of ≥1:40 | 16 (3.6) | 6 (11.1) | 22 (4.4) | 0.023 |
| 3 wk after first dose | ||||
| No. of persons | 383 | 51 | 435b | |
| Geometric mean titer (IQR)a | 70.9 (40-160) | 47.0 (20-160) | 67.1 (40-160) | 0.025 |
| No. (%) of persons with HI titer of ≥1:40 | 310 (80.9) | 36 (70.6) | 346 (79.5) | 0.095 |
| 5 wk after second dose | ||||
| No. of persons | 297 | 44 | 341 | |
| Geometric mean titer (IQR) | 74.2 (40–160) | 53.1 (40–135) | 71.1 (40–160) | 0.049 |
| No. (%) of persons with HI titer of ≥1:40 | 249 (83.8) | 35 (79.5) | 284 (83.3) | 0.52 |
| 7 mo after second dose | ||||
| No. of persons | 121 | 16 | 137 | |
| Geometric mean titer (IQR) | 55.1 (20–80) | 30.8 (20–40) | 51.5 (20–80) | 0.081 |
| No. (%) of persons with HI titer of ≥1:40 | 87 (71.9) | 7 (43.8) | 94 (68.6) | 0.041 |
a
IQR, interquartile range.
b
For one of the patients, the status of the seasonal influenza virus vaccination was missing.