End of season 2022/2023 quadrivalent influenza vaccine effectiveness in preventing influenza in primary care in Portugal

ABSTRACT

Using a test-negative case–control design, we aim to estimate influenza vaccine effectiveness (VE) against medically attended laboratory-confirmed influenza in Portugal in 2022/2023 season. Between week 41/2022 and week 14/2023, data on 592 patients with influenza-like illness aged 18 or more years old were collected by the national sentinel influenza surveillance system in primary care settings. Of those, 218 were positive for influenza and 374 were negative controls. We estimated seasonal influenza VE as (1-odds ratio)*100% of being vaccinated in laboratory-confirmed influenza cases vs. negative controls using logistic regression model adjusted for age group, sex, presence of chronic conditions, and month of symptoms onset. The seasonal VE was 59.3% (95% confidence interval (CI): 27.3 to 77.3) against any laboratory-confirmed influenza and not statistically significant 44.5% (95% CI: −5.6 to 70.8) against influenza A (H3N2). In the 2022/2023 season, characterized by early and low influenza activity and predominant A (H3N2) circulation, vaccination provided a moderate protection against medically attended laboratory-confirmed influenza in primary care.

KEYWORDS:

• Vaccine effectiveness
• influenza
• primary care
• Portugal
• A(H3N2)

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary data

Supplemental data for this article can be accessed on the publisher’s website at https://doi.org/10.1080/21645515.2023.2263219.

Additional information

Funding

The part of the data of the study was originally collected as part of the project “Vaccine effectiveness against COVID-19 and seasonal influenza among patients presenting to primary care physicians in EU/EEA” (Contract ECD.12850 Lot5 (Primary Care)), funded by the European Centre for Disease Prevention and Control through a service contract with Epiconcept “Vaccine Effectiveness, Burden and Impact Studies (VEBIS) of COVID-19 and Influenza” Contract [ECDC/2021/019].