Are Your Symptoms Sign of a Cold, the Flu or COVID-19?

It’s understandable if every cough or sniffle brings on fears of COVID-19. After all, the symptoms associated with familiar illnesses, like a cold and the flu, can also be signs of a coronavirus infection. With reports of breakthrough infections among people who are vaccinated — and the spread of the delta variant, which is more contagious than earlier forms of the coronavirus — many people are on edge.  

That’s why, if you’re feeling sick in the next few months, experts stress the importance of contacting your health care provider, who can determine whether you should be tested for COVID-19 and/or the flu. If you have the flu, you could be treated with an antiviral medication, which works best when taken within two days of your becoming ill. If you have COVID-19, you’ll want to watch for serious symptoms and, of course, follow Centers for Disease Control and Prevention (CDC) guidelines for quarantining to avoid infecting others. 

It’s important to get tested even if you’ve been vaccinated against COVID-19 because you could have a breakthrough infection (even though most cases are mild). The symptoms can be especially hard to differentiate from those associated with a cold or flu. “If you have cold symptoms, you’re not going to know what kind of infection you have,” says Gregory A. Poland, M.D., a professor of medicine and head of the Vaccine Research Group at Mayo Clinic in Rochester, Minnesota.  

In addition to getting the COVID-19 vaccine, be sure to get the flu shot, which may actually lower your susceptibility to the coronavirus while cutting your chances of getting the flu by 40 to 60 percent.

In a study published in Scientific Reports, Mayo Clinic researchers found that people who had received certain vaccines, such as the high-dose flu shot for those over 65, had a lower risk of contracting COVID-19. “Any vaccine causes your immune system to rev up its response,” says Jennifer Johnson, a Mayo Clinic Health System family medicine physician in North Mankato, Minnesota. 

She notes that activating your immune system this way could make it “quicker to respond to COVID.” Other researchers had similar findings. In a study published in the American Journal of Infection Control, people who received the flu shot were less likely to test positive for COVID-19. Those who did contract the coronavirus were less likely to need hospitalization or mechanical ventilation. And if they were hospitalized, they had a shorter stay than those who did not have the flu shot. 

The flu shot also seems to provide protection against COVID-19 complications, such as sepsis, stroke and deep vein thrombosis (a potentially life-threatening blood clot), according to a new study published in PLoS One. In the study, COVID-19 patients who received the flu shot were less likely to visit the emergency department and be admitted to a hospital intensive care unit.

Here’s what doctors know so far about the differences among the three infections and the symptoms to watch for.

A quick comparison of telltale signs

There are no hard-and-fast rules about COVID-19 symptoms because the coronavirus tends to affect people differently. Here’s what experts know now:

• A sudden loss of smell or taste may be the first sign of COVID-19. This symptom seems to occur later and is less pronounced in those with the flu or a cold. However, some doctors are seeing this symptom less frequently in people who have the delta variant.  
  
  
• Flu symptoms tend to strike abruptly, whereas those associated with COVID-19 start out mild and gradually worsen.
  
  
• People who have the flu may be more likely to experience nasal congestion and a productive cough than those with COVID-19. A cough associated with the coronavirus tends to be dry. People who have the delta variant, however, may be less likely to experience a cough. 
  
  
• Shortness of breath is common in people with the flu and COVID-19, but not in those with a cold.
  
  
• Weakness is more common in people with COVID-19 versus the flu.
  
  
• Nausea, vomiting and diarrhea are more common in COVID-19 patients than in those with the flu.