Table 2

Comparison of short and long-term immunity values for influenza A/H1N1 2009 for seasonal influenza vaccine recipients versus nonrecipientsa

Immunogenicity end pointHCWsNHCWs (n = 60)P valuec
Seasonal influenza vaccine recipients (n = 209)Seasonal influenza vaccine nonrecipients (n = 80)P valuebTotal (n = 289)
Seroprotection rate, % (95% CI)
    1 mo postvaccination89.5 (84.6–92.9)92.5 (84.6–96.5)0.5190.3 (86.3–93.2)85.0 (73.8–91.8)0.25
    6 mo postvaccination90.4 (85.7–93.7)91.3 (83.0–95.6)0.8390.7 (86.7–93.5)66.7 (54.0–77.3)<0.01
    10 mo postvaccination53.1 (46.3–59.8)68.8 (57.9–77.8)0.0257.4 (51.7–63.0)61.7 (49.0–72.9)0.57
Seroconversion rate, % (95% CI)
    1 mo postvaccination81.8 (76.0–86.4)81.3 (71.3–88.3)0.9179.9 (74.9–84.1)76.7 (64.5–85.5)0.37
    6 mo postvaccination86.6 (81.3–90.6)87.5 (78.5–93.0)0.8484.0 (79.4–87.8)50.0 (37.7–62.3)<0.01
    10 mo postvaccination45.0 (38.4–51.8)55.0 (44.1–65.4)0.1343.6 (38.0–49.4)46.7 (34.6–59.2)0.54
GMT (95% CI)
    Prevaccination12.7 (11.5–13.9)14.5 (188.0–271.3)0.1613.1 (12.1–14.3)10.5 (8.1–13.6)0.10
    1 mo postvaccination110.7 (94.4–129.9)167.1 (124.2–224.9)0.01124.1 (107.6–143.1)146.1 (97.7–218.6)0.45
    6 mo postvaccination93.9 (81.8–107.7)167.1 (127.8–218.5)<.01110.1 (97.0–125.0)47.4 (33.7–66.7)<0.01
    10 mo postvaccination31.7 (26.7–37.6)55.6 (39.9–77.6)<0.0137.0 (31.7–43.3)40.9 (29.9–55.9)0.60
GMT ratio (95% CI)
    1 mo postvaccination8.7 (7.4–10.3)11.5 (8.4–15.8)0.139.4 (8.1–10.9)13.9 (9.1–21.4)0.09
    6 mo postvaccination7.4 (6.5–8.5)11.5 (8.7–15.2)<0.018.4 (7.4–9.5)4.5 (3.2–6.4)<0.01
    10 mo postvaccination2.5 (2.1–3.0)3.8 (2.7–5.4)0.032.8 (2.4–3.3)3.8 (2.8–5.3)0.10
  • a Geometric mean titer ratios are the ratios of the antibody level at the day of interest compared to that at day 0. Seroconversion was defined as a prevaccination antibody titer of ≤1:10 and a postvaccination titer of ≥1:40. HI, hemagglutination inhibition; CI, confidence interval; GMT, geometric mean titer; HCWs, health care workers; NHCWs, non-health care workers.

  • b Comparison between seasonal influenza vaccine recipients and nonrecipients.

  • c Comparison between HCWs and NHCWs.