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. 2021 Feb;41(2):324-334.
doi: 10.1007/s10875-020-00925-0. Epub 2020 Nov 26.

A Case-Control Study of the 2019 Influenza Vaccine and Incidence of COVID-19 Among Healthcare Workers

Nilofar Massoudi  1 , Babak Mohit  2
Affiliations

A Case-Control Study of the 2019 Influenza Vaccine and Incidence of COVID-19 Among Healthcare Workers

Nilofar Massoudi et al. J Clin Immunol. 2021 Feb.

Abstract

Purpose: The influenza vaccine is essential in reducing the influenza burden, especially among healthcare workers (HCW). Experimental studies suggest both coronaviruses and influenza viruses engage with the angiotensin-converting enzyme 2 (ACE 2) and tetraspanin antibodies, and that ACE 2 tetraspanin antibodies in turn may inhibit both coronavirus and low-pathogenicity influenza A viruses (LP IAV) infections. This study aims to investigate the potential clinical association between receiving the 2019 influenza vaccine and the incidence of COVID-19 among HCW.

Methods: We designed a case-control study within a hospital setting in Iran when it became a center for treating COVID-19 patients. We collected data and calculated relevant incidence and associative measures among HCW who had received the 2019 influenza vaccine as compared to HCW who had not received the vaccine.

Results: Our total sample size was 261 HCW. Of 80 COVID-19 incident cases, three cases had received the influenza vaccine, while 87 of 181 controls had received the vaccine. The odds ratio (OR) and confidence interval (CI) of being vaccinated were 0.04 (95% CI: 0.01 to 0.14) among COVID-19 cases as compared to controls.

Conclusions: Significant findings suggest that the 2019 influenza vaccine may have a protective association against COVID-19 among HCW.

Keywords: COVID-19; case–control; coronavirus; healthcare workers; influenza; vaccine.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Forest plot depicting the odds ratio (OR) and 95% confidence interval (CI) of the association between the incidence of COVID-19 and parameters considered. The horizontal line separates factors in the study. The upper panel is the factors related to the entire sample of healthcare workers (HCW) as enumerated in Table 2 and Table 4, while the lower panel depicts factors related to the subsample of tested HCW enumerated in Table 3 and Table 5. The horizontal axis is a measure of odds ratio (OR) and is on a logarithmic scale. The dotted vertical line is a depiction of OR = 1. Points in the middle of the colored lines (each representing the odds ratio associated with one factor) depict the point estimate of the OR (quantified before the parentheses in the legend), while points at the left and right ends depict the extremes of the 95% confidence interval (quantified within the parentheses in the legend). The colored lines that do not cut through the dotted line indicate statistical significance. The OR reveals a significant association between the incidence of COVID-19 and the 2019 influenza vaccine both among the upper panel (n = 261 enrolled HCW), and the lower panel (n = 83 HCW)
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