What’s Going on with the Flu?
Last week, I was talking to a friend about concerns epidemiologists voiced over potential clashes between COVID-19 and the flu. It reminded me of the tropical storms Laura & Marco — two already fierce storms joining to become one deadly mix. Disease experts fear potentially bad outcomes if patients contract both illnesses simultaneously, creating a Fujiwhara effect in the world of infectious diseases.
The official flu season doesn’t start for another couple of months, so time will tell if this concern comes to fruition. However, the good news is the flu season hasn’t clashed with COVID-19 at this point. In fact, what we have seen since the spring are sharp declines in influenza cases. Of course, the number of flu cases normally declines at the end of spring as the flu season ends, but this year the numbers were additionally impacted by measures taken to prevent the spread of COVID-19 (Broadfoot, 2020).
In January 2020, Dr. Anthony Fauci, of the National Institute of Allergies and Infectious Diseases, warned of the potentially long and harsh flu season. At that time, the B strain, normally showing up in February or March, began months earlier. The flu season in 2019–2020 was expected to be one of the worst seasons in decades (“2019–2020 Flu Season…,” 2020).
In week five of 2020 (late January), the Center for Disease Control (CDC) reported 21,773 new positive tests of the flu (types A and B combined) in the U.S. In comparison, the same week the prior year had only 10,879. There were more than double the number of flu cases nationally compared with the year before (CDC, 2020).
That was around the same time when the WHO declared a global health emergency due to the coronavirus pandemic. A day later President Trump restricted travel from China to help stop the global spread of COVID-19 (Taylor 2020). Americans were told to change some of their practices to help prevent the spread of this new novel virus.
Less than a month later, Italy began to see an increase in coronavirus cases. By the end of February, the U.S. reported the first known death from COVID-19. We were being told to wash our hands and wipe down surfaces by scientists.
Masks were in short supply, so it wasn’t easy to buy them and States had not yet mandated wearing them in public. Even so, flu numbers started to decline slowly, probably due to a better awareness of handwashing. By the first week in March, CDC reported a 33% decrease in positive flu tests (A & B strains combined). The previous year's flu season saw a 20% increase in positive tests over the same period.
On March 13, President Trump declared a national emergency in response to rising cases of COVID-19 in the U.S. (Taylor 2020). Schools were canceled, sports were canceled, businesses closed. That week, positive tests for A and B flu strains dropped again to just over 5,000 nationally. This represented a 74% drop from the season’s peak.
When states began issuing orders to stay at home, the number of positive flu cases dropped again, as expected. The week of April 20, 2020, there were only 28 reported positive tests of influenza A & B. By August, less than ten cases per week were reported.
Below is a graph representing positive tests reported to the CDC of both A and B flu strains combined. You can see what happened with flu numbers when more extreme measures were taken to deal with the spread of COVID-19:
Why the sudden decline?
Although both the flu and COVID-19 are transmitted through droplets produced from coughing, sneezing, or even talking, COVID-19 is more infectious. This is likely because, in addition to spreading through droplets, COVID-19 can be airborne — spread in tiny droplets that remain in the air for much longer (Maragakis, 2020).
Additionally, influenza has a shorter incubation period and a shorter serial interval (the time between successive cases), according to the World Health Organization.
As a consequence, our behavioral changes to help lessen the spread of coronavirus have also decreased the spread of the flu — perhaps even more effectively. Hand washing, social distancing, and wearing masks seem to be effective in preventing the spread of both illnesses.
This doesn’t mean we should skip our flu shots, however. Although the two illnesses share some symptoms, the way they infect the body is different. Scientists are still unsure whether the outcomes of having both simultaneously will lead to extreme outcomes (Broadfoot, 2020). It isn’t worth finding out the hard way.
In short, what is happening to the flu is a nugget of good news. Fingers crossed our diligence with preventing the spread of COVID-19 will continue to suppress influenza numbers as we head into the 2020–2021 flu season. We certainly don’t need one more thing to add to the calamity of 2020.
Note: I love hearing your comments. Please share your thoughts, but let's keep it non-political.
2019–2020 Flu Season on Track to Be Especially Severe, New CDC Data Suggests. (2020, January 4). Time Magazine. https://time.com/5758953/flu-season-2019-2020/
Derrick Bryson Taylor. (2020, August 6). A Timeline of the Coronavirus Pandemic. The New York Times. https://www.nytimes.com/article/coronavirus-timeline.html
Weekly U.S. Influenza Surveillance Report. Centers for Disease Control and Prevention (CDC). https://www.cdc.gov/flu/weekly/index.htm
Marla Broadfoot. (2020, June 4). Coronavirus and the Flu: A Looming Double Threat. Scientific American. https://www.scientificamerican.com/article/coronavirus-and-the-flu-a-looming-double-threat/
Lisa Lockerd Maragakis, M.D., M.P.H. (2020, September 1). Coronavirus Disease 2019 vs. the Flu. John Hopkins Medicine. https://www.hopkinsmedicine.org/health/conditions-and-diseases/coronavirus/coronavirus-disease-2019-vs-the-flu