Table 3.
Indirect Effectiveness of Trivalent Inactivated Influenza Vaccine in Preventing Laboratory-confirmed Symptomatic H3N2 Influenza Among Non-vaccinees, by Age Group
| IIV3 Villages | IPV Villages | ||||||
|---|---|---|---|---|---|---|---|
| Age Groupa | Cases, n | N | Cumulative Incidenceb | Cases, n | N | Cumulative Incidenceb | Adjusted VEIc % (95% CI) |
| <6 months | 49 | 1082 | 4.53 | 49 | 1064 | 4.61 | 7.0 (−59.2 to 45.6) |
| 6 months through 10 years | 114 | 1945 | 5.86 | 120 | 1959 | 6.13 | 7.6 (−29.2 to 33.9) |
| 11 through 17 years | 45 | 2773 | 1.62 | 68 | 2672 | 2.54 | 45.1 (−1.6 to 70.4) |
| 18 through 49 years | 53 | 6065 | 0.87 | 57 | 5667 | 1.01 | 0.3 (−74.6 to 43.1) |
| 50 through 64 years | 30 | 1750 | 1.71 | 19 | 1686 | 1.13 | −35.5 (−135.1 to 21.9) |
| >64 years | 8 | 728 | 1.10 | 6 | 677 | 0.89 | … |
Abbreviations: CI, confidence interval; IIV3, trivalent inactivated influenza vaccine; IPV, inactivated poliovirus vaccine; n, number of cases; N, number of children followed; VEI, indirect effectiveness.
aThe age was unable to be determined for 10 unvaccinated residents of IIV3 villages and 8 unvaccinated residents of IPV villages.
bPer 100 persons through the entire surveillance period: 15 July 2009 through 28 May 2010.
cEstimated using a logistic regression model fit, using generalized estimating equations, assuming an exchangeable correlation matrix to account for within-village correlation of participant observations.