Study Indicates Flu Shot May Protect Against Severe Effects of COVID-19


Patients with COVID-19 who were vaccinated against the flu were found to be significantly less likely to visit the emergency department and be admitted to the intensive care unit.

The flu vaccine has the potential to provide vital protection against COVID-19, according to new research from the University of Miami Miller School of Medicine.

The study, which analyzed de-identified patient records on a global scale, strongly suggests that the annual flu shot reduces the risks of stroke, sepsis, and deep vein thrombosis (DVT) in patients with COVID-19. Those with COVID-19 who have been vaccinated against the flu were also significantly less likely to visit the emergency department (ED) and be admitted to the intensive care unit (ICU), according to the study.

“Only a small fraction of the world has been fully vaccinated against COVID-19 to date, and with all the devastation that has occurred due to the pandemic, the global community still needs to find solutions to reduce morbidity and mortality,” said senior study author Devinder Singh, MD, chief of plastic surgery and professor of clinical surgery at the Miller School, in a press release.

The research team conducted the study using patient records from several countries, including the United States, the United Kingdom, Germany, Italy, Israel, and Singapore. The team used the TriNetX research database to screen de-identified electronic health records for more than 70 million patients to identify 2 groups of 37,377 patients. The 2 groups were then matched for factors that could influence their risk of susceptibility to severe COVID-19, such as age, gender, ethnicity, smoking, and health problems (including diabetes and obesity).

The first study group had received the flu vaccine 2 weeks and 6 months prior to being diagnosed with COVID-19, whereas those in the second group also had a positive COVID-19 diagnosis but were not vaccinated against the flu. The incidence of 15 adverse events (AEs) within 30, 60, 90, and 120 days of testing positive for COVID-19 were then compared between the 2 groups.

The results revealed that those who had not had the flu shot were significantly more likely to have been admitted to the ICU. Further, they were significantly more likely to visit the ED (58%), to develop sepsis (45%), have a stroke (58%), and DVT (40%), and the risk of death was not reduced.

In addition, the researchers were able to calculate how many COVID-19-positive patients would need to receive an influenza vaccine to avoid an adverse outcome. They found that 176 patients needed to have received a flu vaccine to prevent an ED visit within 120 days of testing positive for COVID-19. With this, only 286 patients needed to have received their flu vaccine to prevent 1 case of sepsis. For every 440 patients who were updated on their flu shot, 1 ICU admission was prevented.

These results suggest that the flu vaccine may protect against several severe effects of COVID-19, but the study authors strongly recommend that the public should get their COVID-19 vaccines as well as their annual flu vaccine. Although more research is needed, the researchers said they hope the flu shot can provide increased protection in countries where the COVID-19 vaccine is in short supply or help protect against new breakthrough cases in individuals who are already vaccinated against COVID-19.

“Continued promotion of the influenza vaccine also has the potential help the global population avoid a possible ‘twindemic’—a simultaneous outbreak of both influenza and coronavirus,” said medical student Susan Taghioff, who helped conduct the study, in a press release. “Regardless of the degree of protection afforded by the influenza vaccine against adverse outcomes associated with COVID-19, simply being able to conserve global health care resources by keeping the number of influenza cases under control is reason enough to champion continued efforts to promote influenza vaccination worldwide.”


New study: Flu shot protects against severe effects of COVID-19. EurekAlert! August 4, 2021. Accessed August 5, 2021.

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