COVID-19, Flu, and Allergies: What's the Difference?

You’ve got the sniffles, muscle aches, a runny nose, a sore throat, and a cough. Are these the unpleasant symptoms of the flu? After all, the flu season has arrived. Or maybe you’re allergic to ragweed, the biggest allergy trigger in the fall?

Surely, you don’t have COVID-19. You’re fully vaccinated.

COVID-19 (coronavirus) and flu (seasonal influenza) are both respiratory illnesses, but they are caused by different viruses, explains infectious disease expert Dr. Stephanie Stovall, Chief of Quality and Patient Safety at Lee Health.

“Because some of the symptoms of flu and COVID-19 are similar, it can be difficult to tell them apart,” Dr. Stovall says. “Adding to the challenge is that symptoms sometimes can overlap when COVID-19 and flu are circulating in a community at the same time.”

Let’s not forget allergies from pollen, grass, or pet dander. Allergy symptoms can include runny or stuffy nose, itchy nose or eyes, red eyes or cough. But they typically don’t cause fevers, difficulty breathing, muscle aches, diarrhea, nausea, or vomiting, Dr. Stovall says.

Parents shouldn’t automatically assume their child has COVID-19, the flu, or an allergy. Testing, says Dr. Stovall, is the only way to confirm a diagnosis.

COVID-19 symptoms

COVID-19 seems to cause more serious illnesses in some people, according to the Centers for Disease Control and Prevention (CDC). Other signs and symptoms of COVID-19, different from flu, may include a change in or loss of taste or smell.

If you’re infected with COVID-19, you’ll typically develop symptoms five days after infection. However, symptoms can appear as soon as two days after infection or as late as 14 days after infection.

Learn about the symptoms of COVID-19 here.

Influenza symptoms

If you’re infected with the flu, symptoms typically develop one to four days after infection.

People who have the flu often experience some or all the following symptoms, which can be found here.

Avoid a ‘twindemic’: Get your flu vaccination

According to the Florida Department of Health, flu cases in Florida dropped to a record low last year thanks to COVID-19 preventive practices such as wearing masks, social distancing, and sanitizing our hands. Like COVID-19, the flu spreads mainly through respiratory droplets transmitted by coughing, sneezing, and talking. People with the flu can spread the virus up to six feet away.

However, experts this fall fear a spike in flu infections because pandemic protocols have relaxed, and we’ve returned to workplaces and schools. The possibility of a “twindemic” – a severe flu season combined with the ongoing pandemic – underscores the need for everyone six months and older to get this year’s flu vaccine, according to Dr. Stovall. She adds that vaccination is particularly important for people who are at high risk of serious complications from influenza.

“Getting re-vaccinated for the flu each season is necessary because flu strains are constantly changing – the immunity we had against a particular strain of flu last year won’t necessarily recognize a strain circulating in the community this year,” Dr. Stovall notes. “Our immunity from the vaccination also declines over time. Although the vaccine isn’t a 100 percent guarantee that you won’t get the flu, it’s still the safest and best way to protect yourself and others against influenza – especially severe infection.”

Dr. Stovall answers some questions:

Q: I already got a COVID-19 vaccine. Do I really need a flu shot, too?

A: Yes. COVID-19 vaccines prevent the coronavirus, and flu vaccines prevent influenza. They don’t overlap. But you can catch both viruses at the same time, or one after the other.

“Avoid the double whammy” and get both vaccines, as the American College of Emergency Physicians advises. For now, COVID-19 vaccines are available for anyone 12 and older.

People vaccinated with the flu vaccination, if they do get the flu, tend to have a much milder illness. That’s also true for people vaccinated against COVID-19 who get breakthrough infections. Their infections generally are less severe than if they hadn’t been vaccinated against COVID-19.

Q: Can I get a flu vaccine and a COVID-19 vaccine at the same time?

A: Yes, the CDC says it’s safe to pair a flu vaccine with either a primary COVID-19 shot or a booster dose.

Q: What’s the best flu vaccine available?

A: Because flu constantly evolves, each year’s vaccine is made to fight the strains most likely to circulate. This year’s flu vaccine offers protection against all four of the strains currently circulating. You can decide to get a traditional shot or a nasal spray vaccine.