“There’s a refrain that ‘COVID-19 is just the flu,’ which is not at all accurate.
“Andrew Pekosz, PhD, says it can be hard to differentiate the two based on symptoms alone. But large numbers of susceptible people and increased rates of severe disease and death set COVID-19 apart from seasonal influenza. Pekosz, a leading virologist who works on both diseases, breaks down key differences between COVID-19 and influenza to show why this pandemic is so critically—and catastrophically—dangerous.
“What would you say to someone who insists to you that COVID-19 is ‘just the flu’?
“Since December 2019, COVID-19 has killed more people in the U.S. than influenza has in the last five years. Influenza is a significant burden on the population, but COVID-19 has had a vastly larger effect.
“Are people more susceptible to COVID-19 or the flu?
“Many more people are susceptible to COVID-19 because there is little preexisting immunity to the virus that causes it—SARS-CoV-2. Through vaccinations and previous infections, a portion of the population has some immunity to influenza, which helps limit the number of cases we see each year. There is a lot of similarity between how the two viruses are spread, but the number of susceptible people is really what allows SARS-CoV-2 to spread so easily.
“If infected, which has the higher rate of severe disease and mortality? How much higher?
“COVID-19 has a higher severe disease and mortality rate than influenza in all age groups, except perhaps children under the age of 12.
“Are the populations at higher risk for severe COVID-19 disease the same as the populations at higher risk for severe flu?
“There is some overlap. The elderly and individuals with cardiovascular disease or a high BMI have more severe disease with both infections. It looks like children and pregnant women are more susceptible to severe disease with influenza, but it’s not clear why that is.
“What makes COVID-19 particularly dangerous?
“First, little preexisting immunity to SARS-CoV-2 means that virtually everyone is susceptible to infection. Second, we don’t have good treatments or vaccines for SARS-CoV-2 like we have for influenza. Third, COVID-19 causes more severe disease than influenza overall.
“Are there long-term health effects of the flu? How do they compare to increasing evidence about long-term health effects of COVID-19?
“This is another area where the two viruses differ. COVID-19 survivors report many more long-term effects of the infection than influenza survivors. Lingering symptoms like weakness, shortness of breath, trouble focusing and, in some cases, kidney and heart problems are much more common after COVID-19 than after influenza. ‘Mild’ COVID-19 illness has been described as ‘flu-like.’ It’s important to remember that the flu is a pretty debilitating disease so ‘mild’ COVID-19 is still a pretty significant disease.
“If so many people get only ‘mild’ illness with COVID-19, how can it be more dangerous than the flu?
“With all infectious diseases, we focus on two main objectives:
1. Treat the infected people
2. Limit the spread of the infection in the population.
“A large number of COVID-19 patients present with no or very mild symptoms, but those individuals can still transmit the virus to others, some of whom could have a much more serious course of illness. Every person who gets infected keeps the ‘chains of transmission’ going, which can bring COVID-19 to those who are more vulnerable.
“Is it possible to contract COVID-19 and the flu at the same time, and if so, how dangerous would that be?
“There have been very few reports of one person infected with both viruses. But we know that COVID-19 has been spreading when influenza has not been detected, so it’s still not clear how big of a risk a co-infection would pose. There was very little influenza in the Southern Hemisphere’s winter (corresponding to the Northern Hemisphere’s summer), but that could be because public health interventions like social distancing and masks worked against influenza. Here in the U.S., we aren’t controlling COVID-19 well enough with public health interventions, so that may open the door for spread of influenza. Since the symptoms are difficult to differentiate, you need to be tested to see if you have SARS-CoV-2, influenza, or perhaps one of the other half dozen or so respiratory infections that usually circulate in fall and winter” (John Hopkins, Bloomberg School of Public Health).