Effect of the 2020/21 season influenza vaccine on SARS-CoV-2 infection in a cohort of Italian healthcare workers. Issue 12 (15th March 2022)

• Record Type: Journal Article
• Authors: Domnich, Alexander; Orsi, Andrea; Sticchi, Laura; Panatto, Donatella; Dini, Guglielmo; Ferrari, Allegra; Ogliastro, Matilde; Boccotti, Simona; De Pace, Vanessa; Ricucci, Valentina; Bruzzone, Bianca; Durando, Paolo; Icardi, Giancarlo
• Is Part Of: Vaccine. Volume 40:Issue 12(2022)
• Page Start: 1755
• Page End: 1760
• Publication Date: 2022-03-15
• Subjects: Influenza -- Vaccination -- Influenza vaccines -- SARS-CoV-2 -- COVID-19 -- Healthcare workers; Vaccines -- Periodicals; 615.372
• DOI: 10.1016/j.vaccine.2022.02.013
• Languages: English
• ISSNs: 0264-410X

Abstract

Highlights: Healthcare workers are at high risk of both influenza and SARS-CoV-2 infections. Influenza vaccines may exercise non-specific effects by inducing the trained immunity. Higher SARS-CoV-2 testing frequency is associated with higher positivity rate. Lower risk of SARS-CoV-2 was observed among recipients of influenza vaccines. Influenza vaccination should be further encouraged among healthcare workers. Abstract: Objectives: Healthcare workers (HCWs) are a priority group for seasonal influenza vaccination (SIV). The 2020/21 SIV campaign was conducted during the second wave of the COVID-19 pandemic. Vaccines, including SIV, may exert non-specific protective effects on other infectious diseases which may be ascribable to the concept of trained immunity. The aim of this study was to explore the association between 2020/21 SIV and SARS-CoV-2 positivity in a cohort of Italian HCWs. Methods: In this observational study, a cohort of HCWs employed by a large (ca 5000 employees) referral tertiary acute-care university hospital was followed up retrospectively until the start of the COVID-19 vaccination campaign. The independent variable of interest was the 2020/21 SIV uptake. Both egg-based and cell culture-derived quadrivalent SIVs were available. The study outcome was the incidence of new SARS-CoV-2 infections, as determined by RT-PCR. Multivariable Cox regression was applied in order to discern the association of interest. Results: The final cohort consisted of 2561 HCWs who underwent ≥1 RT-PCR test and accounted for a total of 94, 445 person-days of observation. SIV uptake was 35.6%. During the study period, a total of 290 new SARS-CoV-2 infections occurred. The incidence of new SARS-CoV-2 was 1.62 (95% CI: 1.22–2.10) and 3.91 (95% CI: 3.43–4.45) per 1000 person-days in vaccinated and non-vaccinated HCWs, respectively, with an adjusted non-proportional hazard ratio of 0.37 (95% CI: 0.22–0.62). E -values suggested that unmeasured confounding was unlikely to explain the association. Conclusions: A lower risk of SARS-CoV-2 infection was observed among SIV recipients.