Scientists Find No Link Between Flu Vaccination And Reduced Risk Of Covid-19

(ORDO NEWS) — A large study of more than 46,000 Danish health workers found no link between influenza vaccination and a reduced risk of coronavirus infection or hospitalization due to Covid-19.

The Department of Cardiology and Emergency Medicine at the University Hospital of Copenhagen and the University of Copenhagen (Denmark) have not been able to confirm that influenza vaccination has an effect on reducing the risk of contracting coronavirus. The study is published in The Journal of Infectious Diseases .

Previously, scientists assumed that immunity to the influenza virus could provide protection against Covid-19 and hospitalization due to it due to the similarity of immune responses: for example, a study of doctors from Taiwan showed a 28 percent decrease in the likelihood that a patient with SARS-CoV-2 will need mechanical ventilation, and a 24 percent drop in the risk of infection. Therefore, at the dawn of the current pandemic, it was recommended to be vaccinated against influenza for prevention.

The authors of the new study decided to revisit previous arguments and understand how influenza vaccination affects the risk of hospitalization due to Covid-19 and the infection itself. They have screened for SARS-CoV-2 antibodies among staff at multiple healthcare facilities in Copenhagen and the Zeeland region of Denmark.

Blood samples were taken three times: from April 15 to May 7, 2020, from June 2 to 10, and from September 30 to October 7. In addition, all participants filled out an online questionnaire about hospitalization and symptoms related to Covid-19, general health status and availability of a flu shot for the 2018-2019 or 2019-2020 season.

Initially, the sample included 60,681 people under the age of 65, but later it decreased to 46,112 people: more than 36,000 of them were women, the average age was 44-46 years, the body mass index was 24.22, and almost 10,000 were smokers.

Participants who were vaccinated against the flu were older, more educated, and had more comorbidities than those who were not vaccinated. In total, 3379 people were ill with Covid-19: they were either treated in hospitals or had obvious symptoms of coronavirus infection.

Adjusted for age, chronic illness (diabetes was most common), smoking status and other factors, the adjusted risk of hospitalization due to SARS-CoV-2 for people who received the flu vaccine was 0.89-0.91 compared with unvaccinated.

The likelihood of symptomatic Covid-19 for vaccinated people was estimated at 1.16-1.24. The chances that those vaccinated against Influenza Virus will in principle have antibodies to coronavirus were 1.00-1.06.

In addition, the researchers analyzed a group of 1,841 participants over 65 years of age: in their case, the risk of infection, which was determined by the presence of antibodies, was 0.93-0.99 for those vaccinated against influenza compared to those who did not receive the vaccine.

As with younger people, scientists have not found any significant effect of influenza vaccination on the likelihood of hospitalization or the development of Covid-19 symptoms at any time of the year.

“To our knowledge, this is the first large-scale study to assess the impact of influenza vaccination on the severity of coronavirus-related illness in healthcare workers.

Previous data on its nonspecific protective effects were at variance. <…> In our work, having a flu shot did not change the risk of hospitalization or symptoms of Covid-19 and was not associated with the risk of SARS-CoV-2 infection, “the scientists concluded.

Of course, the design of this study also has limitations: firstly, information about the severity of Covid-19 is based only on the results of a survey completed by the participants themselves. In addition, confusion cannot be ruled out: influenza vaccination in Western countries is more common among people with better health insurance or more aware of their health.


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