Table 3.
Influenza vaccine effectiveness in preventing outpatient cases with laboratory-confirmed influenza.
| Cases/Controls | Crude Vaccine Effectiveness, % (95% CI) | Adjusted Vaccine Effectiveness, % (95% CI) a | p-Value | |
|---|---|---|---|---|
| All outpatients | ||||
| Unvaccinated | 196/238 | 1 | 1 | |
| Vaccinated | 26/98 | 68 (48 to 80) | 48 (8 to 70) | 0.026 |
| Aged 9 to 64 years | ||||
| Unvaccinated | 189/216 | 1 | 1 | |
| Vaccinated | 15/39 | 56 (18 to 76) | 45 (−7 to 72) | 0.077 |
| Aged ≥65 years | ||||
| Unvaccinated | 7/22 | 1 | 1 | |
| Vaccinated | 11/59 | 41 (−70 to 80) | 48 (−83 to 85) | 0.312 |
| Target population | ||||
| Unvaccinated | 58/93 | 1 | 1 | |
| Vaccinated | 22/86 | 59 (27 to 77) | 47 (−8 to 73) | 0.080 |
| A/H3N2 subtype b | ||||
| Unvaccinated | 107/183 | 1 | 1 | |
| Vaccinated | 15/77 | 67 (39 to 82) | 50 (−4 to 76) | 0.063 |
| A/H1N1 subtype c | ||||
| Unvaccinated | 17/164 | 1 | 1 | |
| Vaccinated | 6/80 | 28 (−91 to 72) | 7 (−233 to 74) | 0.908 |
| B type d | ||||
| Unvaccinated | 66/116 | 1 | 1 | |
| Vaccinated | 1/53 | 97 (75 to 99) | 88 (3 to 98) | 0.046 |
Abbreviations: CI, confidence interval. a Vaccine effectiveness adjusted by sex, age groups (9–24, 25–44, 45–64, 65–84, and ≥85 years), presence of major chronic conditions, and month of sample collection. b The analysis of A/H3N2 covered the period October 2022 to February 2023. c The analysis of A/H1N1 covered the period December 2022 to March 2023. d The analysis of B covered the period January to April 2023.