If you have a runny nose, sore throat and/or aching muscles does that mean you have a cold, the flu or COVID? The frustrating answer is you could have any of the above. The symptoms of these three illnesses are often alike, especially with the current dominant omicron variant that tends to attack the upper respiratory tract rather than the lungs. And now with flu season in full swing, it is difficult to distinguish what is making you ill.

Experts warn that this flu season can be severe since last year’s case rate fell 98% due to COVID-19 measures and we didn’t develop sufficient immunity. And researchers have found that the current influenza vaccine doesn’t match the dominant strain of the flu virus, giving us even more reason to be worried.

As omicron spreads throughout the country, its hallmark symptoms closely resemble that of the common cold and the flu. While vaccinated people are not likely to experience severe illness that requires hospitalization from omicron, Dr. Abdul El-Sayed, a noted epidemiologist, tells CNN that infections should be taken seriously.

“Just because the per-individual risk of severe illness may be lower, that doesn’t mean on a societal level omicron doesn’t pose a real risk,” he said. “Even a small proportion of a relatively large number can be a relatively large number.”

Dr. Sarah Ash Combs, a pediatric emergency medicine specialist in Washington, D.C., said that since the symptoms of all three viral illnesses are similar, the only sure way to diagnose is to test.

“Short of getting a test, I would say it’s really tricky to distinguish right now,” she said. “We need to just treat cold-ish symptoms in pretty much the same bucket” as COVID.

El-Sayed explains that early signs of cold, flu and COVID-19 are comparable. Symptoms of flu and COVID-19 include fever, fatigue, body aches, sore throat and shortness of breath, along with vomiting and diarrhea according to the Centers for Disease Control and Prevention.

“Because some of the symptoms of flu, COVID-19, and other respiratory illnesses are similar, the difference between them cannot be based on symptoms alone,” says the CDC. “Testing is needed to tell what the illness is and confirm a diagnosis.”

However, COVID-19 infection is often identified by the headache and dry cough that accompany it, says CNN. The loss of taste and smell that have been classic signs of coronavirus can also help narrow the diagnosis, but this is less prevalent with omicron, says El-Sayed.

He warns that individuals who experience serious chest pain with a dry cough that worsens, should seek medical help.

“If you are starting to feel any of these symptoms, it’s worth asking: Has anybody with whom I’ve come into contact been infected with COVID? It’s also worth isolating and taking a rapid test,” he told CNN. El-Sayed recommends taking a test when you have symptoms or five days after exposure to the disease. He cautions that if you test negative, continue to isolate, and retest in a day or two to make sure that you don’t have COVID-19.

El-Sayed, the former executive director of the Detroit Health Department, says that with all viral illnesses it is a good idea to isolate, and even more so with the increasing spread of COVID-19. He acknowledged that this advice could change as we learn more about omicron.

“It’s changing quickly. We’re learning a lot more,” he told CNN. “Omicron is a variant we’ve really only known for about a month.”