Table 6.
Evolution of DRIVE studies from 2017–2018 to 2021–2022 influenza seasons.
| Influenza season | 2017–2018 | 2018–2019 | 2019–2020 | 2020–2021 | 2021–2022 |
|---|---|---|---|---|---|
| Characteristics | High influenza circulation | Moderate influenza circulation | Moderate influenza circulation—study capped by COVID-19 emergence | No influenza circulation—COVID-19 pandemic | Very low influenza circulation—late influenza epidemic peak (March–April 2022) Omicron COVID-19 pandemic |
| Study network | 5 study contributors 4 countries +950 GP 4 hospitals | 10 study contributors 7 countries 377 GP 12 hospitals | 14 study contributors 8 countries 388 GP 19 hospitals | 14 study contributors 8 countries +500 GP 25 hospitals | 13 study contributors 8 countries +1,000 GP 21 hospitals |
| Number of subjects | 5,475 (TND) 288,655 py cohort Finland | 9,351 (TND) 768,414 py cohort Finland | 9,077 (TND) 511,854 py cohort Finland | 7,025 (TND) 857,095 py cohort Finland | 6,315 (TND) 836,622 py for cohort Finland |
| Number of LCI | 2,844 (TND) 13,300 (cohort Finland) | 3,339 (TND) 6,379 (cohort Finland) | 3,500 (TND) >2,400 (cohort Finland) | 4 (TND) 25 (cohort Finland) | 1,039 (TND) 331 (cohort Finland) |
| Brand-specific IVE estimates (brands captured/brands marketed in EU/EEA/UK) | 4/11 | 7/10 | 8/11 4 precise* brand-specific IVE estimates | Did not reach threshold to trigger IVE estimation | 8/12 |
GP, general practitioner; py, person-years; LCI, laboratory-confirmed influenza; py: person-years; TND, test-negative design.
*Precise: Brand-specific IVE estimates below the threshold of confidence interval width <40%, arbitrarily agreed upon by DRIVE researchers.