Even as the death toll from COVID-19 climbs, there are people out there claiming the threat of the novel virus is being exaggerated and that it’s really no worse than a bad flu.
While it’s true that both are caused by viruses that are respiratory in nature and both have the potential to cause symptoms like coughs and fevers, it’s becoming increasingly clear they are not all that similar.
Their differences start with the packaging the viruses come in, and they continue through the way they attack people’s immune systems, even onto how deadly they are. Here’s a look at how they’re different and why.
They’re caused by different types of viruses
Influenza and coronavirus are two different families of viruses. While they both are made up of RNA (some diseases’ genetic material is DNA), the protein layers that surround the RNA, causing the immune response, are different in the two pathogens.
Influenza’s shell features hemagglutinin and neuraminidase proteins. Coronaviruses get their name from the glycoprotein spikes that surround them, giving them a crown-like appearance under magnification. Those different surface proteins interact differently with human cells.
Many types of common colds are coronaviruses, as are severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). COVID-19 is more closely related to those viruses than influenza.
The flu has been around for a long time, and we know a lot about it
Historians say the flu may date back millennia. Some of the first written descriptions of the virus are thought to date back to Hippocrates, around 410 BCE.
The influenza virus itself was identified in 1933, so people have had a long time to figure out how the flu works. We know when it’s likely to hit each year, and we know who’s more susceptible to severe complications.
“We know a lot about the flu. It’s got seasonality. We know what time of year it hits. We know that pregnant women, older people and young kids are at particularly high risk,” said Dr. David Ingbar, a professor of medicine, the director of the pulmonary, allergy, critical care and sleep division at the University of Minnesota’s Medical School and Executive Director of the Center for Lung and Science Health.
It’s not clear yet whether or to what degree COVID-19 will have a seasonal element, either. It could quiet down over the summer, or (perhaps more likely) it may not.
With COVID-19, patterns are emerging that suggest people who are older or have underlying conditions are at higher risk of severe complications, but much is still being learned — even every week, as the medical community learns more about the virus and even identifies new symptoms, like loss of taste and smell and rashes.
COVID-19 appears to be more transmissible
One of the numbers underpinning policy discussions about COVID-19 is something called an R0. Pronounced “R-naught,” this number refers to how many other people, on average, a person with a given virus will infect.
For seasonal influenza, the R0 is thought to be between 0.9 and 2.1, meaning the average infected person will infect one or two others. The Minnesota COVID-19 model currently predicts an R0 of 3.87, meaning the average infected person infects about 3.9 others. That means COVID-19 is more infectious than the flu.
Flu also has a shorter incubation period than COVID-19. It usually between one and four days for someone infected with the flu to show symptoms. With COVID-19, the incubation period may be up to 14 days, making it more likely people will spread the virus before they show symptoms.
COVID-19 is often asymptomatic
When Minnesota Department of Health researchers unveiled Version 3 of their COVID-19 model Wednesday, they increased the share of infections assumed to be asymptomatic from 25 percent to 41 percent. That’s a lot of people who could be walking around and infecting others without even knowing it.
If you get the flu, on the other hand, you tend to get the flu — you show symptoms. There isn’t the same degree of asymptomatic carriers walking around with the flu without knowing it.
“Some individuals are reporting very mild illness due to COVID-19, and flu is usually pretty miserable for everyone,” said Melissa McMahon, a senior MDH epidemiologist working in vaccine-preventable disease surveillance, in an email.
For people who do have symptoms of COVID-19, there’s a range of them, from a headache to being wiped out to loss of taste, a skin rash and having a cough. Some, but not all, people seem to get fevers.
“I think of influenza as being more consistent in general,” Ingbar said.
COVID-19 is more deadly
It’s been tough for researchers to get a handle on the death rate of COVID-19, partly because so many people seem to be getting it without showing symptoms.
Early estimates in China put the death rate at around 3 percent. Recent research put the mortality rate in the U.S. around 1.3 percent, or a little over one in 100 infections.
That might not seem terribly high, but it’s much higher than a seasonal flu, which typically sees death rates around 0.10 percent, or one in 1,000 infections.
That suggests COVID-19 is about 10 times more fatal than a seasonal flu.
Some strains of flu are more deadly than others. The influenza virus is able to mutate quickly, and new strains have varying success at evading the human immune response.
“One part is immunity in how much your body recognizes it and defends against it. The other part is the mutation sometimes gives the virus extra potency, an ability to replicate more effectively or kill cells more easily,’ Ingbar said.
In terms of specific strains, flu tends to be deadlier in years where the A H3 strain is dominant, versus the A H1 strain. The A H3 strain is particularly severe for people over 65, McMahon said.
In Minnesota, there have been 683 confirmed deaths due to COVID-19 as of Friday morning. That’s four times higher than the number of people — 153 — believed to have died of flu so far this flu season. It’s one-third higher than the number of people who died of flu in 2017-18, a particularly deadly year when A H3 was prevalent, but Minnesota is believed to have yet seen the peak of COVID-19 cases and deaths.
Deaths from flu and COVID-19 in Minnesota by year
Note: Figures for 2019-20 cover flu season through May 9. Figures for COVID-19 in Minnesota include lab-confirmed deaths through May 15.
Source: Minnesota Department of Health
While COVID-19 is more deadly than influenza, people shouldn’t downplay the dangers of the flu, Ingbar said.
Ingbar said he sometimes has to work hard to convince patients to get a flu shot, particularly if they aren’t in any high-risk groups. Sometimes they cite imperfect rates of effectiveness, but even so, people who get flu shots significantly cut their chances of getting sick and feeling miserable for two weeks.
And some years more than others, the flu really can present risks to people’s lives.
“People forget that the flu itself can be a pretty serious illness,” Ingbar said.