Finding the difference: COVID-19 and the flu

“Have you had any flu-like symptoms?” is a routine question regarding COVID-19, but with flu season at the door, the line between the two illnesses is growing thinner.

As influenza season approaches, many experts worry about how cases of influenza will affect the ongoing COVID-19 pandemic.

“The most common symptoms of both COVID-19 and influenza can’t be distinguished. These symptoms are fevers, chills, weakness and cough,” said Judy Streit, M.D., a clinical professor of internal medicine and infectious diseases at the University of Iowa.

Nevertheless, there are some differences between the symptoms of these two diseases.

There are some symptoms for COVID, like loss of sense of taste and smell, that aren’t common for flu.”

— Aaron Miller

“There are some symptoms for COVID, like loss of sense of taste and smell, that aren’t common for flu,” said Aaron Miller, an assistant professor of Epidemiology at the University of Iowa.

Even with similar symptoms, there are many differences between the two diseases. About five days after the onset of symptoms, someone with influenza will start to recover. However, someone with COVID-19 might start to experience complications such as pneumonia, heart inflammation, neurologic symptoms, or blood clots. Some of these symptoms can occur with influenza as well, but some of these complications are more common with COVID-19.

“There are some things that might point more towards coronavirus,” said Jeanenne Suneja, a clinical assistant professor of internal medicine at the University of Iowa. “Number one, right now, we know that the flu is not really circulating in the Midwest area. Another is exposure. Did you get exposed to anyone with Coronavirus and did you develop symptoms? Also, did you lose your sense of taste and smell? That tends to be fairly specific for coronavirus.”

While both diseases have a similar range of symptoms, COVID-19 appears more contagious than influenza. While someone with influenza may only transmit the disease for three to five days after the onset of symptoms, people with COVID-19 may be contagious two to three days before any sign of symptoms, and almost a week after symptoms occur. However, because COVID-19 is new, many details about the epidemiology of the disease have yet to be fully determined. 

Another important topic concerning these two diseases is vaccination. While a vaccine for COVID is still in testing stages, vaccines for influenza have been around for decades and are available each year. In order to help protect patients and healthcare workers, most staff at hospitals are required to get an influenza vaccine every year, unless they have had a previous adverse reaction to the vaccine. 

There are two major strains of influenza, A and B. Even within a strain, there is differentiation, and the influenza virus mutates rapidly. Thus, to design the influenza vaccination, “[Vaccine producers] look ahead to other parts of the world where the flu circulates kind of ahead of us … and then they kind of make some predictions. And then they pick the most common strains,” said Suneja. 

[Vaccine producers] look ahead to other parts of the world where the flu circulates kind of ahead of us … and then they kind of make some predictions. And then they pick the most common strains.”

— Jeanenne Suneja

Because of this guesswork, the influenza vaccine is not perfect. Despite this, getting a vaccination for influenza is still beneficial. Last year, the vaccine was about 50 percent effective.

“In a good year of maybe 60 percent, but it’s not uncommon when you don’t have a good match that your efficacy rates might be 40 percent or 50 percent. There is also some data that indicate that even if people get the flu or are diagnosed with the flu if they’ve had the vaccine they may not have as severe an illness as those people who haven’t been vaccinated,” said Streit.

There is some data that indicate that even if people get the flu or are diagnosed with the flu if they’ve had the vaccine, they may not have as severe an illness as those people who haven’t been vaccinated.”

— Judy Streit

The high mutation rate of the flu makes creating a completely effective vaccine impossible. To date, these complications do not appear to apply to COVID-19. While this pandemic has lasted almost a year, no drastic mutations have occurred, which has made the creation of a vaccine much easier than it would be otherwise, and will cause the vaccine to be much more effective than the influenza vaccination. Although not available yet, a vaccine for COVID-19 is currently in trial stages. In order to be approved, this vaccine will not only need to be safe but will also be required to be at least 51 percent effective at preventing infection. Some experts predict that this vaccine will be ready in December or sometime next year. 

“Pfizer [recently announced that] their trial had positive results showing that it is 90 percent effective,” said Miller.

“The challenge is going to be how to distribute it,” Streit said. “Some of the vaccines have to be kept at very very cold temperatures and so it may have to be kind of in special places with their special planning of how they’re going to deliver it to the public.”

Another important aspect of both diseases is reinfection. While coming into contact with the infection can help your immune system to fight off the disease a second time, getting infected with COVID twice is still possible, though unlikely. 

“Most of the time, it’s probably multiple months after their first illness. And sometimes it’s difficult to prove [reinfection]. But it wouldn’t be a big surprise because we know what other sorts of coronaviruses have been circulating with humans for a long time. We know that sometimes the immunity that develops doesn’t last very long,” Streit said.

Thankfully, this flu season is predicted to be less severe than years past. This is because influenza is spread in the same way as COVID-19, through contact. And so, if social distancing, handwashing and mask-wearing are enforced and followed, they will slow down the spread of both of these diseases simultaneously.