An analysis of historical data shows there is no evidence that the influenza vaccine increases an individual’s risk of coronavirus. Four coronaviruses are known to cause the common cold and were used in this analysis to help assess whether the flu vaccine is likely to interact with COVID-19.
The analysis was completed using data from the Canadian Sentinel Practitioner Surveillance Network (SPSN), a network headquartered at the BC Centre for Disease Control (BCCDC) and led by Dr. Danuta Skowronski. The analysis included data from the 2010/11 influenza season through to the 2016/2017 influenza season during which time patient samples were tested for both influenza and other non-influenza respiratory viruses (NIRVs), including coronaviruses.
The analysis included 4,281 influenza, 2,565 non-influenza respiratory viruses, and 3,841 negative specimens from patients in four provinces and compared the findings with information on whether the patients had received their influenza vaccine. Overall, they found the vaccine significantly reduced the risk of influenza illness by more than 40 per cent but had no effect on other causes of respiratory illness including infections due to coronaviruses.
“Next season’s annual influenza vaccine will provide important protection against influenza viruses at a time when people will be at risk for seasonal illness due to a number of different respiratory viruses including COVID-19,” said Skowronski, lead of the Influenza and Emerging Respiratory Pathogens team at the BCCDC. “There is no reason to believe that the influenza vaccine will affect your risk of COVID-19 infection.”
Using what is called a test-negative design, investigators assessed the effects of influenza vaccine on the risk of illness with fever and cough due to influenza virus or other NIRVs. Developed by Skowronski's team in 2004, the test-negative design is used globally to monitor influenza vaccine effects by comparing the odds of having been vaccinated among cases who tested positive for influenza or other respiratory viruses to that of controls who test negative for those viruses.
The analysis was completed after a widely-shared study out of the United States in January suggested that the influenza vaccine could potentially increase the risk of illness from coronavirus.
The Canadian analysis used more seasons' data spanning seven years. By correcting the issues in the U.S. analysis, the Canadian findings provide reassurance against the speculation that influenza vaccine may negatively affect COVID-19 risk.