Effectiveness of Influenza-Prevention Interventions among Healthcare Workers: A Systematic Review and Meta-Analysis of Health Outcomes

Abstract

Background: Although studies do not provide conclusive evidence of their benefits, influenza vaccinations and face masks are recommended and even mandated to prevent influenza infections in Healthcare Workers (HCWs).

Objectives: To summarize the latest evidence on the effectiveness of influenza prevention interventions in HCWs.

Methods: We systematically searched PubMed, Scopus and Google Scholar for RCTs, cohorts and cross-sectional studies published in English up to 30 September 2024. All studies comparing groups of HCWs with and without intervention/exposure were included. Three reviewers independently selected articles and extracted data. Estimates were pooled using random-effects meta-analyses. Pooled analyses were conducted on outcomes including Laboratory-Confirmed Influenza (LCI), Influenza-Like Illness (ILI) and work absenteeism.

Main results: Twenty-one articles met eligibility criteria. For influenza vaccine, three articles were RCTs, twelve were cohort and three were cross-sectional studies; and for face masks, there was one RCT, one cohort and one cross-sectional study. The pooled results showed an insignificant effect of influenza vaccine and face masks on the incidence of laboratory-confirmed influenza (RR=0.68, 95% CI: 0.36-1.27) and ILI (RR=0.23, 95% CI: 0.03-1.68). A subgroup analysis showed that vaccination significantly reduced the incidence of LCI in small samples (<30 participants), but not in large samples. In addition, influenza vaccination was not associated with reducing the incidence of ILIs (RR=1.04, 95% CI: 0.84-1.29). However, it significantly reduced work absenteeism (SMD=0.87, 95% CI: 0.81-0.94). There is insufficient data to assess the effects of wearing a face mask on ILI or workplace absenteeism.

Conclusion: Our findings did not provide conclusive evidence for the effectiveness of influenza vaccination or face masks in reducing influenza infections. Influenza vaccination had a significant benefit in reducing absenteeism in HCWs by 17%. As HCWs play a central role in patient care, it is crucial to ensure the safety and protection of patients. Therefore, understanding the clinical need for influenza protection while applying other practical measures such as hand hygiene and other personal protective equipment is essential. High-quality RCTs are needed to evaluate the final impact of these protective measures in different clinical settings and parts of the world.

Abbreviations: CDC: Centers for Disease Control and Prevention; GISRS: The WHO's Global Influenza Surveillance and Response System; HCWs: Healthcare Workers; IIV: Inactivated Influenza Vaccine; ILI: Influenza-Like Illness; LAIV: Live Attenuated Influenza Vaccine; LCI: Laboratory-Confirmed Influenza; MD: Mean Difference; NOS: Newcastle-Ottawa Scale; PI/ECO: Population, Intervention/Exposure, Comparison and Outcome; PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analysis; RCTs: Randomized Controlled Studies; RIDT: Rapid Influenza Test; RR: Risk Ratio; WHO: World Health Organization.