Effectiveness of influenza vaccine among health care personnel in Thailand, 2018/19 season

Abstract

Abstract Background Influenza vaccination is the most effective way of preventing influenza infections and it is recommended for the entire health care personnel in Thailand. However, the evidence of influenza vaccine effectiveness (VE) among health care personnel is lacking in Thailand. The objective of this study was to estimate influenza vaccine effectiveness (VE) against laboratory confirmed medically attended influenza illness for the 2018/9 season among health care personnel who at risk for influenza infection in Bangkok, the capital of Thailand. Methods Throat swab specimens were collected from patients with influenza-like illness (ILI) presenting to outpatient clinics and tested for influenza virus by RT-PCR, between October 2018 and September 2019. A test-negative case-control design was used to estimate influenza VE against medically-attended laboratory-confirmed influenza in outpatient settings. Cases were influenza-like illness (ILI) patients who tested positive for influenza, and controls were influenza negative patients. Results During the 2018/19 season 373 samples were collected; 57 (15.3%) were positive for influenza, 70.2% A un-subtyped and 29.8% B. Adjusted VE against all influenza viruses for this influenza season was -31.7% (95% confidence interval (CI): -40.2 to 66.4), against influenza A un-subtyped, it was 43.9% (95% CI: -30.6 to 75.9) and against influenza B, it was 52.0% (95% CI: (-73.9 to 86.8). Conclusions The seasonal influenza vaccine was moderately effective against medically attended lab-confirmed influenza infection in health care personnel in Bangkok, Thailand in the 2018-19 influenza season. Key messages The seasonal influenza vaccine was moderately effective against medically attended lab-confirmed influenza infection in health care personnel in Bangkok. Increasing seasonal influenza vaccination among health care personnel in Thailand may decrease medically attended influenza-associated ILI cases in this population.