Flu Vaccine May Reduce Some of the Severe Effects of COVID-19, New Study Finds

In the largest study of its kind, patients with COVID-19 who did not receive flu vaccine were significantly more likely to visit the emergency department and to have a stroke, among other severe effects.

The influenza vaccine may reduce the risk of stroke, sepsis, and deep vein thrombosis (DVT) in patients with COVID-19, according to new research being presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID), held online between July 9 and July 12, 2021.

Flu vaccination also reduced the risk of emergency department (ED) visits and admission to the intensive care unit (ICU).

"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 author Devinder Singh, MD, professor of plastic surgery, University of Miami Miller School of Medicine, in a press release.

There have been reports based on several modestly-sized studies that suggest the flu vaccine may be protective against COVID-19, according to the release.

To explore the possibility further, Singh and colleagues screened de-identified electronic health records of over 70 million patients and identified two groups of 37 377 patients each to be included in the study.

The retrospective data analysis was global and included participants from various countries including the US, United Kingdom, Germany, Italy, Israel, and Singapore.

The 2 groups were matched for factors that could affect their risk of severe COVID-19, including age, gender, ethnicity, smoking, diabetes, obesity, and chronic obstructive pulmonary disease.

Patients in the first group had received the influenza vaccine between 2 weeks and 6 months before being diagnosed with COVID-19. Patients in the second group had also been diagnosed with COVID-19 but were not vaccinated against influenza.

Researchers compared the incidence of 15 adverse outcomes within 120 days of testing positive for COVID-19 between the 2 groups:

  • Sepsis
  • Stroke
  • DVT
  • Pulmonary embolism
  • Acute respiratory failure
  • Acute respiratory distress syndrome
  • Arthralgia
  • Renal failure
  • Anorexia
  • Myocardial infarction
  • Pneumonia
  • ED visits
  • Hospital admission
  • ICU admission
  • Death

Researchers found that patients who had not received the flu jab (group 2) were approximately 20% more likely to have been admitted to the ICU compared to those who had been vaccinated against influenza (group 1).

Patients in group 2 were also approximately 58% more likely to visit the ED and approximately 45% more likely to develop sepsis, compared to those in group 1. Also, patients in group 2 were up to 58% more likely to have a stroke and nearly 40% more likely to have a DVT, compared to those in group 1.

The risk of death was not reduced between the 2 groups, according to the press release.

These results are, “particularly significant because the pandemic is straining resources in many parts of the world. Therefore, our research - if validated by prospective randomised clinical trials - has the potential to reduce the worldwide burden of disease," said Singh in the press release.

However, the researchers stressed that the influenza vaccine is, “by no means a replacement for the COVID-19 vaccine and we advocate for everyone to receive their COVID-19 vaccine if able to,” said lead author Susan Taghioff, assistant professor of chemistry, University of Miami Miller School of Medicine, in the same press release. "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.”

"Regardless of the degree of protection afforded by the influenza vaccine against adverse outcomes associated with COVID-19, simply being able to conserve global healthcare resources by keeping the number of influenza cases under control is reason enough to champion continued efforts to promote influenza vaccination,” added Taghioff.