Trivalent Influenza Vaccine Reduces Risk of Severe COVID-19, Especially Among High-Risk Groups, Finds Study

A new study of COVID-19 patients has demonstrated that a recent trivalent flu vaccine reduces the odds of severe disease, ventilator support requirement, and death, indicating that such vaccines must be used widely to reduce the risk of severe COVID-19, especially among high-risk groups.

The study examined the outcomes in over 92,000 COVID-19 patients in Brazil, who had and had not been given flu vaccinations recently. The researchers found that the mortality in the non-immunized group rose from about 14% in the under-10 age group to 84% among those aged 90 years and above. However, the mortality was lower in all age groups in the immunized group, with the risk being 17% lower in the 10-19 years age group and 3% less in those aged 90 years and above. The study also looked at the age-influenza vaccine relationship and found that among vaccinated patients, there was a significant reduction by over a third in the odds of dying of COVID-19 at 35%, while the odds of dying of COVID-19 was lower by 18%.


Among patients with a positive RT-PCR-proved COVID-19 diagnosis, the association between lower mortality and flu vaccination remained significant. Those with obesity and lung disorders, as well as renal and kidney disorders had a higher risk of death, while those with asthma faced a lower risk. Additionally, patients who had received flu vaccination had 8% lower odds of requiring intensive care and about 20% fewer odds of needing respiratory support. The patients vaccinated in the current round were found to be protected but not those vaccinated earlier. Patients who had been vaccinated before developing symptoms of COVID-19 showed a 20% reduction in the odds of mortality, while there was a 27% reduction in the odds of death in those who had been vaccinated after the onset of symptoms.

The study demonstrates that while influenza vaccines do not increase the risk of adverse outcomes among COVID-19 patients, they do have a protective effect, possibly through several mechanisms. In their study published on the preprint server medRxiv, the researchers have suggested: “Given the high similarities of SARS-CoV-2 and influenza viruses with respect to viral structure, transmission, and pathogenic mechanisms, it seems plausible that both viruses are detected by similar or identical pattern recognition receptors. Their binding to viral RNA can then trigger suitable inflammatory and antiviral responses.”

The study concludes: “In the absence of a COVID-19 vaccine and without a well-established treatment to avert disease progression, induction of trained immunity exerting beneficial, off-target effects might be a fruitful avenue for improving COVID-19 outcomes. Governments should seriously consider promoting flu vaccination at this time in view of the many benefits since reducing the number of severe COVID-19 cases will help relieve the strain on the healthcare system and allow the sickest patients to receive adequate care.”