Table 3. Comparison of the effect estimates of influenza vaccination from different models with the estimate that compares people vaccinated in the current season with those unvaccinated in the current and five previous seasons, Navarre, Spain, pooled analysis of 2011/12–2018/19 influenza seasons (n = 10,356).
| Vaccination effect | Absolute difference of vaccination effect in % | ||
|---|---|---|---|
| % | 95% CI a | ||
| All patients | |||
| Summarised model with five previous seasons | 40 | 33–47 | Reference |
| Summarised model with three previous seasons | 39 | 32–45 | −1 |
| Summarised model with one previous season | 36 | 29–43 | −4 |
| Only-current-season model | 31 | 23–38 | −9b |
| Primary healthcare patientsc | |||
| Summarised model with five previous seasons | 40 | 27–51 | Reference |
| Summarised model with three previous seasons | 39 | 25–50 | −1 |
| Summarised model with one previous season | 37 | 23–48 | −3 |
| Only-current-season model | 35 | 21–47 | −5b |
| Hospitalised patients | |||
| Summarised model with five previous seasons | 39 | 30–47 | Reference |
| Summarised model with three previous seasons | 38 | 29–46 | −1 |
| Summarised model with one previous season | 36 | 27–44 | −3 |
| Only-current-season model | 29 | 19–37 | −10b,d |
| Age 9–64 yearsc | |||
| Summarised model with five previous seasons | 45 | 35–54 | Reference |
| Summarised model with three previous seasons | 46 | 34–53 | 1 |
| Summarised model with one previous season | 43 | 32–52 | −2 |
| Only-current-season model | 42 | 31–51 | −3 |
| Age ≥ 65 years | |||
| Summarised model with five previous seasons | 35 | 24–44 | Reference |
| Summarised model with three previous seasons | 34 | 23–44 | −1 |
| Summarised model with one previous season | 32 | 21–41 | −3 |
| Only-current-season model | 24 | 13–33 | −11b,d |
| Influenza A(H1N1) | |||
| Summarised model with five previous seasons | 53 | 42–61 | Reference |
| Summarised model with three previous seasons | 50 | 39–60 | −3 |
| Summarised model with one previous season | 51 | 40–59 | −2 |
| Only-current-season model | 47 | 36–56 | −6b |
| Influenza A(H3N2) | |||
| Summarised model with five previous seasons | 24 | 11–34 | Reference |
| Summarised model with three previous seasons | 24 | 13–35 | 0 |
| Summarised model with one previous season | 21 | 9–32 | −3 |
| Only-current-season model | 14 | 2–25 | −10b,d |
| Influenza Bc | |||
| Summarised model with five previous seasons | 53 | 42–61 | Reference |
| Summarised model with three previous seasons | 50 | 39–59 | −3 |
| Summarised model with one previous season | 47 | 35–56 | −6b |
| Only-current-season model | 44 | 32–53 | −9b |
CI: confidence interval.
a Vaccination effect adjusted by age groups (9–44, 45–64, 65–84 and ≥ 85 years), major chronic conditions, healthcare setting (primary healthcare and hospital) and month and season of sample collection.
b Absolute difference of vaccine effect of at least ± 5% was considered as a bias.
c The results of this model should be considered with caution since there was a negative interference between vaccination in the current and previous seasons.
d Absolute difference of vaccine effect of at least ± 10% was considered as a relevant bias.