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[Effectiveness of annual flu vaccination until week four of season 2018/2019].

OBJECTIVE
Annual flu vaccination is the most effective measure to prevent the disease and its complications. Vaccine effectiveness (EV) varies from season to season, requiring annual re-evaluation. The objective of this work was to estimate the preliminary effectiveness of the influenza vaccine until epidemiological week 4 of the 2018/2019 season, in patients admitted to a third level hospital.


METHODS
The Test Negative Design (TDN) was carried out at the Hospital General Universitario de Alicante. Patients admitted with laboratory-confirmed influenza (RT-PCR positive for any influenza virus, in clinical sample of nasopharyngeal aspirate) and those with clinical suspicion of influenza and negative RT-PCR, from week 40 to week 4 of the 2018/2019 influenza season, were considered as controls. The vaccination coverage was calculated in the cases and in the controls, and the EV with its 95% confidence interval using the formula: EV = (1-Odds Ratio) x 100.


RESULTS
We included 524 patients: 58 cases and 466 controls. The overall EV for prevention of influenza cases was 42.5 % (95% CI -17.1 to 71.8) and for those over 1 year of age 63.7 % (95% CI 25.4 to 82.3).


CONCLUSIONS
The 2018-2019 influenza vaccine is effective in preventing influenza cases in patients admitted up to week 4 of the 2018-19 season. Results are preliminary and may vary and should be re-evaluated at the end of the season.