Health-care workers who received the influenza vaccine were also protected against COVID-19, however, the effect may be temporary. Influenza vaccines have an unanticipated health benefit: they may aid in the prevention of COVID-19, particularly in its more severe symptoms.

According to a study of over 30,000 healthcare workers in Qatar, individuals who received a flu vaccine were more than 90% less likely to develop severe COVID-19 over the next several months than those who had not previously been inoculated against flu.

The study, which was done in late 2020, before the COVID-19 vaccines were made available, is consistent with previous research suggesting that strengthening the immune system with influenza vaccines and other vaccinations could help the body fight the coronavirus. SARS-CoV-2. 

Beneficial Bystander

While COVID-19 vaccines were still being produced in the early months of the pandemic, researchers were anxious to see if current vaccinations may provide some protection against SARS-CoV-2. Obtaining solid proof for such an effect, however, is difficult since people who seek immunization for diseases other than COVID-19 may also make other decisions that reduce their risk of developing SARS-CoV-2.

Researchers led by Laith Jamal Abu-Raddad, an infectious-disease epidemiologist at Weill Cornell Medicine–Qatar in Doha, evaluated the health records of 30,774 medical professionals in the country to lessen the consequences of the ‘healthy-user effect.’ According to Abu-Raddad, such workers have less variation in health-related behavior than the general population, which decreases — but does not eliminate — prejudice.

The researchers followed up on 518 workers who tested positive for SARS-CoV-2 and compared them to almost 2,000 study participants who tested negative. When compared to workers who did not receive an influenza vaccine that season, those who did were 30% less likely to test positive for SARS-CoV-2 and 89% less likely to develop severe COVID-19 (although the number of severe cases was small in both groups). The report was published on the med aRxiv preprint service on May 10.

Günther Fink, an epidemiologist at Switzerland’s University of Basel, feels the Qatar study reduces the possibility that prior research that discovered the same link was a fluke. His team discovered that flu vaccines were associated with a decreased risk of death among COVID-19 hospitalized patients in Brazil.

“This is critical proof,” says Mihai Netea, an infectious-disease specialist at Nijmegen’s Radboud University Medical Center. He adds that the fact that influenza vaccines are related to a decrease in not just SARS-CoV-2 infections but also disease severity demonstrates that the protection is genuine.

Time Limitation

It is unknown how long this shield will last. SARS-CoV-2 infections were detected six weeks after vaccination in individuals in the Qatar study who received the flu shot and then contracted COVID-19. “I don’t think this effect will last long,” he predicts. Netea expects the advantages to last between six months and two years.

It’s unknown why flu vaccines manufactured from dead influenza viruses might also protect against COVID-19. According to Netea, who has witnessed such reactions in flu vaccine recipients, vaccines not only teach the immune system to recognize specific viruses but also strengthen broad-acting antiviral defenses.

Netta’s team also intends to investigate the efficacy of COVID-19 vaccinations against influenza and other diseases. To rule out healthy-user effects, his team has started a randomized, placebo-controlled trial in Brazil to examine if influenza and measles–mumps–rubella vaccines can protect against COVID-19.

According to Netea, knowing that flu and other illness vaccines can protect COVID-19, albeit only partially and for a limited time, could reduce the damage caused by a future pandemic until a vaccine for that disease is created. “You could save millions of lives if you had something in place from the start.”

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