School of Medicine

How to Tell the Flu from COVID-19

Tufts’ director of infection control describes the similarities and differences, and explains why getting the flu vaccine is so important for you—and those around you
“The best time to get a flu shot is anytime you can,” says Michael Jordan. “If you want to time it closer to the typical flu season, October is ideal.” Photo: iStock

With the advent of fall comes the flu season—and the potential for it to make the rounds in the midst of the current pandemic. But how do you differentiate between the flu, caused by the influenza virus, and COVID-19? And what can you do to avoid the flu?

For answers, Tufts Now spoke with Michael Jordan, A94, M98, who is the infection control director for Tufts University, an assistant professor of medicine as well as of public health and community medicine at the School of Medicine, and an attending physician in the Division of Infectious Diseases and Geographic Medicine at Tufts Medical Center.

Jordan, who is board certified in infectious diseases, says the best way to avoid the flu is to get the vaccine, as soon as you can. “If you wait for the perfect time, you may forget altogether and miss the benefits of an annual flu shot, which generally prevents 50 to 60 percent of influenza infections in a typical season,” he says.

Tufts Now: How can you tell if your symptoms are from the flu—or even a common cold—and not COVID-19?

Michael Jordan: Flu is caused by the influenza virus and COVID-19 is caused by a novel coronavirus called SARS-CoV-2. Both cause respiratory illness, but the viruses are different. Because some of the symptoms of flu and COVID-19 are similar, diagnostic testing may be needed to help confirm a diagnosis. But there are some key differences between the two.

Flu and COVID-19 cause similar symptoms, ranging from none—the infected person is asymptomatic—to severe symptoms. Common symptoms of both COVID-19 and flu include:

  • Fever or feeling feverish or having chills
  • Cough
  • Tiredness
  • Sore throat
  • Muscle pain or body aches
  • Headache
  • Shortness of breath or difficulty breathing
  • Vomiting or diarrhea, though this is more common in children than adults

There are some important differences. Change or loss of taste or smell are highly specific for COVID-19. If you experience change or loss of taste or smell, contact your health care provider—you may need a diagnostic test for COVID-19. If your only symptom is a runny or stuffy nose, it is likely a common cold or perhaps the flu, but unlikely to be COVID-19.

Is the flu transmitted differently from COVID-19?

The modes of transmission are largely the same. Therefore wearing of masks, physical distancing—staying six or more feet away from others—and proper hand hygiene decrease the risk of both infections.

When does flu season typically run in the U.S.?

Flu season in the United States generally starts in early to mid-October and usually peaks from December to March.

Is there a good time in the fall to get the flu vaccine to maximize its effectiveness?

The best time to get a flu shot is anytime you can. If you wait for the perfect time, you may forget altogether and miss the benefits of an annual flu shot, which prevents 50 to 60 percent of influenza infections in a typical season. If you want to time it closer to the typical flu season, October is ideal. Remember that your body needs about two weeks after the vaccination to develop a protective responsive to the influenza virus, so it’s best to get the vaccination before the influenza rate begins to climb.

Some people who get the flu vaccine might think if they get flu-like symptoms, it must be COVID-19—but could they in fact be getting a milder version of the flu?

The effectiveness of the annual flu vaccine varies from year to year, generally ranging from 40 to 70 percent. So, it is possible to have received a flu shot and still get the flu. Most importantly, the flu shot has been shown to prevent severe disease and risk of hospitalization.

So, yes, you may get a milder case than if you had not been vaccinated. Additionally, the flu vaccine is an important preventive tool for people with chronic health conditions and helps protect women during and after pregnancy. Getting vaccinated yourself also protects those around you, especially those more vulnerable to serious flu illness, like young children, older people, and people with certain chronic health conditions.

To make sure we’re all really clear on this: the flu vaccine won’t protect you from COVID-19, right?

That’s right! The flu vaccine will not protect you from COVID-19; however, flu vaccination has many other important benefits. Flu vaccines reduce the risk of flu illness, hospitalization, and death. Getting a flu vaccine this fall will be more important than ever, not only to reduce your risk from flu but also to help conserve limited health care resources. To minimize the likelihood that you get either COVID-19 or the flu, continue to practice social distancing, wear a mask, and follow good hand hygiene practices.

What measures beyond getting the flu vaccine, masking, washing hands, and social distancing can we take to avoid getting the flu?

Getting a good night’s sleep every night, maintaining a healthy and balanced diet, and ensuring optimal management of chronic medical conditions, such as diabetes, can help.