Seasonal influenza vaccine effectiveness among health-care workers in Prince Sultan Military Medical City, Riyadh, KSA, 2018–2019

Background: Healthcare Workers (HCWs) constitute a major group exposed to influenza. Researchers herein try to determine the influenza vaccine effectiveness (VE). Influenza VE depends on the vaccinated personal characteristics and the closeness of matching between the vaccine and the prevalent strains of the virus. The aim of our research was to identify the 2018–2019 seasonal influenza VE in HCWs. Methods: a record-based study was carried out using the test-negative design from October 2018 to September 2019 to calculate the influenza VE. HCWs with influenza like illness (ILI) were screened to detect the positive cases, and the vaccination status was determined based on vaccination database. VE was assessed from the ratio of the odds of vaccination among positive cases to the odds of vaccination among negative controls. Statistical analysis Multivariable logistic regression was used to estimate adjusted VE Results: a total of 556 HCWs presented with ILI, 65.6% were females, and 54.1% were nurses, 152 HCWs (27.3%) had laboratory-confirmed influenza, shows two peaks in January and March 2019. VE for all types was 35.0% and rose to 42.0% after adjustment for HCWs age, gender, nationality, and job position, influenza A (H3N2) VE was 78.0%. H1N1 VE was 55.0% but no significant VE for type B was found. Conclusion: Our VE estimates are in agreement with VE estimates published for that season. The use of quadrivalent vaccine with two stains of influenza B is recommended.