Impact of the influenza vaccine on COVID-19 infection rates and severity

Abstract

Background With a unique influenza season occurring in the midst of a pandemic, there is interest in assessing the role of the influenza vaccine in COVID-19 susceptibility and severity. Methods In this retrospective cohort study, patients receiving a laboratory test for COVID-19 were identified. The primary outcome was comparison of positive COVID-19 testing in those who received the influenza vaccine versus those who did not. Secondary end points in patients testing positive for COVID-19 included mortality, need for hospitalization, length of stay, need for intensive care, and mechanical ventilation. Results A total of 27,201 patients received laboratory testing for COVID-19. The odds of testing positive for COVID-19 was reduced in patients who received an influenza vaccine compared to those who did not (odds ratio 0.76, 95% CI 0.68 to 0.86; P < 0.001). Vaccinated patients testing positive for COVID-19 were less likely to require hospitalization (odds ratio, 0.58, 95% CI 0.46 to 0.73; P < 0.001), or mechanical ventilation (odds ratio, 0.45, 95% CI 0.27 to 0.78; P = 0.004) and had a shorter hospital length of stay (risk ratio, 0.76, 95% CI 0.65 to 0.89; P <0.001). Conclusion Influenza vaccination is associated with decreased positive COVID-19 testing and improved clinical outcomes and should be promoted to reduce the burden of COVID-19.

Examining the potential benefits of the influenza vaccine against SARS-CoV-2: A retrospective cohort analysis of 74,754 patients

“…This timespan enabled our study to include data from the 2019–2020 influenza vaccine formulation as well as the most recent 2020–2021 influenza season formulation. This contrasts with the timespan of the previously mentioned study, as well as the recently published retrospective review of 27,000 patients by Conlon et al Both of these studies analyzed SARS-CoV-2 cases between March-August 2020, a period overlapping between two different influenza vaccinations and seasons which excludes peak influenza season, and did not set a 2 week– 6 month time limit for influenza vaccine being “current/active” [ 9 , 12 ]. Additionally, the Yang and Conlon study timeframes began 6 months after the CDC’s recommended influenza vaccination time in October, therefore the vaccine antibodies were likely already waning [ 9 , 12 , 20 ].…”

The Association between Influenza Vaccination and COVID-19 and Its Outcomes: A Systematic Review and Meta-Analysis of Observational Studies

“…Among the 41 articles assessed based on full texts, 25 articles were excluded for lacking specific data or did not meet the inclusion criteria. A total of 16 studies were finally included in the review (12 studies on the association between influenza vaccination and SARS-CoV-2 infection [16,18,[21][22][23][24][25][26][27][28][29][30], 6 on the association between influenza vaccination and COVID-19 clinical outcomes [10,17,22,26,31,32], 2 studies containing data on both the associations [22,26]. Nine of the 12 studies on the association between influenza vaccination and SARS-CoV-2 infection contained adjusted estimates.…”

Association between Influenza Vaccination and Positive SARS-CoV-2 IgG and IgM Tests in the General Population of Katowice Region, Poland

“…An important association of SARS-CoV-2 seropositivity and vaccination against influenza was observed in a large study (over 27,000 patients) performed in Michigan (USA). Compared with nonvaccinated patients, the vaccinated group showed a less frequent occurrence of positive tests (OR = 0.82; 95% CI 0.73-0.92), a lower rate of hospitalizations, and a shorter length of in-hospital stay, as well as a decreased need for mechanical ventilation [26].…”