A Preview of Influenza Season 2021: Are We In For a Mega-Flu Winter?

Aug 6, 2021 | Caleb Boyer | Outbreak News

While the public’s focus is largely centered on the emergence of the highly contagious Delta variant of COVID-19, public health experts are simultaneously looking ahead to the coming flu season. 

Last year’s flu season

Flu cases in 2020-2021 were extremely low compared to previous years. Since last September, roughly 2,000 cases of influenza have been lab-confirmed in the United States. In years prior, the average number of confirmed cases was more than 200,000. This decline is not due to a decrease in flu testing, either. 1.3 million specimens have been tested going back to September 2020, compared to an average of 1.0 million during that same period in years prior [1]. 

The decrease in cases could be attributed to a few factors. First, a higher number of Americans were vaccinated against the flu than in any of the four previous seasons – 193.7 million people received the flu vaccine as of March, 2021, compared to only 174.5 million in 2020 [2]. Additionally, since COVID-19 and the flu are both respiratory viruses, public health measures taken to slow the spread of COVID-19, such as wearing face masks and social distancing, likely impacted the transmission of flu as well.

Experts are worried about this winter

Though last year’s relaxed flu season may seem positive, it actually could be a sign to worry for the upcoming winter. Due to the low percentage of the population who had the flu last year, levels of immunity will be much lower than usual. Specifically, children could be at higher risk of getting the flu. Since most childrens’ immune systems have never encountered the virus before, children are more likely to contract the flu in a typical flu season. Thus, without a normal season’s worth of immunity to protect some children, pediatric cases–and, resultantly, deaths–may be especially high [3].

Applying lessons from COVID-19 vaccines

Traditionally, the most common flu vaccines are Inactivated Influenza Vaccines (IIV) and Live Attenuated Influenza Vaccines (LAIV). Inactivated vaccines use a killed version of the flu virus, while attenuated vaccines utilize weakened samples. Neither can cause influenza, though both may produce mild signs or minor side effects.

However, a few companies are currently researching an alternative that uses mRNA. Pfizer, Moderna, and BioNTech all harnessed mRNA in the creation of their COVID-19 vaccines, which were produced much more rapidly than many previous vaccines. Typically, it can take anywhere from 18 months to three years to create a vaccine that can be tested in people. In this instance, using mRNA, researchers were able to do so in just over two months after receiving the genetic sequence of the COVID-19 virus [4,5].

This research comes as there is a lot of room for improved flu vaccine production. Current flu vaccines reduce the likelihood of a doctor visit by 40-60%, but efficacy can drop to nearly zero percent in years when flu variants are widespread [5]. Furthermore, most flu vaccines are egg-based, meaning they are produced through a six-month process that requires growing the target virus inside chicken eggs [6]. More prone to mutations than COVID-19, the flu virus often produces new strains by the time the vaccine is created [5]. The ability to create a vaccine more quickly would give the WHO more time to choose the most important strains to target in vaccine creation, meaning the vaccine could be more effective and flu variants could become less dangerous.

Looking forward

Seqirus, a global vaccine company whose single focus is developing influenza vaccines, recently announced that they have begun to ship 60 million doses of the flu vaccine in preparation for the upcoming flu season [7]. Overall, manufacturers are expected to produce nearly 200 million doses in total. These shots will be distributed in the United States from August until November [8].

Despite preparations for a record level of demand, some experts worry that last year’s success may be hard to repeat. Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, expressed concerns that this season’s flu vaccine campaign may be less effective. 

“Our influenza vaccine campaign will be in some sense competing with COVID-19. Even among people who’ve received the COVID-19 vaccine, there is a kind of vaccine weariness. We have been speaking about vaccination so much I think some of our messaging will fall on deaf ears, ears that in previous years would have been more receptive to the message to get vaccinated against flu,” he said.

Achieving the same vaccination rate as last winter will be difficult if Americans trivialize the flu, especially if those unvaccinated against COVID-19 do not get the flu vaccine. Combined with the fact that much of what minimized the spread of the flu last winter – social distancing, mask-wearing, and travel restrictions – is now gone, we could be headed for a particularly severe flu season.



  1. https://www.nytimes.com/interactive/2021/04/22/science/flu-season-coronavirus-pandemic.html 
  2. https://www.cdc.gov/flu/fluvaxview/dashboard/vaccination-doses-distributed.html 
  3. https://www.nbcnews.com/health/health-news/after-year-virtually-no-flu-scientists-worry-next-season-could-n1266534
  4. https://news.vanderbilt.edu/2021/03/17/shot-in-the-arm-groundbreaking-covid-19-vaccine-research-by-alumnus-dr-barney-graham-began-at-vanderbilt-decades-ago/ 
  5. https://www.wsj.com/articles/the-next-target-for-mrna-vaccines-after-covid-19-the-flu-11627041601  
  6. https://www.cdc.gov/flu/prevent/egg-allergies.htm 
  7. http://outbreaknewstoday.com/flu-vaccines-60-million-doses-being-shipped-according-to-seqirus-70776/ 
  8. https://www.healthline.com/health-news/how-vaccine-hesitancy-could-impact-flu-season-this-year#Getting-a-flu-shot 
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