Table 3.
Effect of previous vaccination on estimates of vaccine effectiveness (VE) in school outbreaks of influenza in Beijing, 1 November 2016 to 30 April 2017.
| Vaccine(s) received | Vaccination status |
VE (%) against any influenza virus |
VE (%) against influenza A(H1N1)pdm09 |
VE (%) against influenza A(H3N2) |
||||
|---|---|---|---|---|---|---|---|---|
| Confirmed casesa No. (Col.%) |
Asymptomatic Controlsb No. (Col.%) |
Unadjusted (95% CI) |
Adjustedc (95% CI) |
Unadjusted (95% CI) |
Adjustedc (95% CI) |
Unadjusted (95% CI) |
Adjustedc (95% CI) |
|
| Overall Unvaccinated |
176 (100) 133 (75.6) |
628 (100) 339 (54.0) |
||||||
| 2015–2016 vaccination only | 13 (7.4) | 60 (9.6) | 46 (−4 to 72) | 46 (−5 to 72) | 50 (−162 to 91) | 56 (−89 to 90) | 43 (−16 to 72) | 39 (−28 to 71) |
| 2016–2017 vaccination only | 14 (8.0) | 145 (23.1) | 77 (58 to 87) | 77 (58 to 87) | 71 (−4 to 92) | 70 (1 to 91) | 80 (59 to 90) | 79 (58 to 90) |
| Both 2016–2017 and 2015–2016 vaccinations | 16 (9.1) | 84 (13.4) | 57 (19 to 77) | 57 (17 to 78) | 44 (−75 to 82) | 46 (−44 to 80) | 67 (27 to 85) | 54 (−6 to 80) |
NOTE. CI: confidence interval; VE, vaccine effectiveness. Vaccine effectiveness was estimated by comparing the vaccination coverage in cases and controls and calculated as 100 × (1 − odds ratio) using conditional logistic regression model.
aConfirmed cases: patients who tested positive for influenza virus in an influenza outbreak included in the study.
bAsymptomatic controls: classmates of cases in an influenza outbreak included in the study who were asymptomatic (i.e., without symptoms of cough, or sore throat) during the period from the illness onset of the index case to the ending of the outbreak.
cAdjusted for age group, sex, areas, BMI, chronic conditions by conditional logistic regression.