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Seasonal influenza vaccine effectiveness against influenza in 2012–2013: A hospital-based case-control study in Lithuania

Gefenaite, Giedre, Rahamat-Langendoen, Janette, Ambrozaitis, Arvydas, Mickiene, Aukse, Jancoriene, Ligita, Kuliese, Monika, Velyvyte, Daiva, Niesters, Hubert, Stolk, Ronald P., Zagminas, Kestutis, Hak, Eelko
Vaccine 2014 v.32 no.7 pp. 857-863
at-risk population, case-control studies, confidence interval, hospitals, influenza, patients, regression analysis, reverse transcriptase polymerase chain reaction, vaccination, vaccines, Lithuania
Due to scarce information on seasonal influenza vaccine effectiveness (SIVE) against severe clinical influenza outcomes in risk populations, we conducted a case-control study to assess its effects against laboratory-confirmed influenza in hospitalized patients during the 2012–2013 influenza season.We conducted a test-negative case-control study among ≥18 years old patients with influenza-like illness (ILI) hospitalized in two Lithuanian hospitals. Cases were influenza A(H1N1), A(H3) or influenza B positive by RT-PCR, and controls were influenza negative. Additional demographic and clinical data to assess the role of confounding were collected. SIVE and its confidence intervals (95% CI) were estimated by using multivariate logistic regression as (1−OR)×100%.The sample consisted of 185 subjects. Seasonal influenza vaccine uptake was 5%. Among 111 (60%) influenza positive cases, 24.3% were A(H1N1), 10.8% were A(H3) and 24.3% were influenza B cases. Unadjusted SIVE was 79% (95% CI −6% to 96%) and after the adjustment it increased to 86% (95% CI 19% to 97%).Seasonal influenza vaccination in 2012–2013 was associated with reduced occurrence of laboratory-confirmed influenza, but due to low sample size the estimate of SIVE is imprecise. Given high prevalence of influenza in hospitalized ILI cases and low influenza vaccination coverage, there is a need to increase influenza vaccination rates.