RELATED: If You Have Omicron, This Is When You’ll Begin to Feel Symptoms. It can be hard to differentiate between COVID, cold, and flu symptoms, especially with Omicron causing the majority of new infections. But Bruce Patterson, MD, a virus expert and founder of cell diagnostic company IncellDX, told the Deseret News that there is one symptom that is consistent among all of the COVID variants, including Omicron. “The one thing that’s always present with COVID is fatigue,” he explained. And amid a surge of new Omicron cases, Patterson said there was another symptom he is spotting more and more. “I’m seeing a lot of headaches,” he added. Fatigue and headache can be symptoms of other illnesses, but with Omicron spreading so rapidly and producing breakthrough infections, these two symptoms indicate you should get tested for the virus—especially if you know you’ve been exposed to someone with COVID. “It’s worth isolating yourself and getting a couple of tests,” epidemiologist Abdul El-Sayed, MD, told CNN. “Don’t test immediately after you might have been exposed. Once you’re getting symptoms, you want to test one day, and then test again the next day just to be sure as you’re isolating.” RELATED: Dr. Fauci Says This Is How the Pandemic Will End Now. Not having certain tell-tale COVID signs doesn’t mean you don’t have the virus, however. “I haven’t seen a lot of the tremendous shortness of breath [with Omicron],” Patterson said. And according to Patterson, other once common COVID symptoms are not as likely with the variant. In fact, data from the U.K. COVID Symptom Study has found that Omicron appears to show a departure from “the classic three” COVID symptoms of fever, cough, and loss of smell or taste. Researchers in Norway reported similar data among breakthrough Omicron cases after a large Christmas party. Out of 87 confirmed or probable cases, only over half reported a fever, 23 percent experienced loss of taste, and just 12 percent had a decline in smell. Not many people are experiencing loss of smell or taste with the Omicron variant. But this was a strong sign of the Delta variant, which is still circulating in the U.S. According to the CDC, 58.6 percent of infections in the country are estimated to be the result of Omicron—meaning that around 40 percent are likely to be caused by the formerly dominant Delta. “Loss of taste and smell is another common and distinguishing feature, though some studies suggest there may be less cough and loss of taste and smell with the Delta variant compared to the ancestral strain,” Joyce Sanchez, MD, Froedtert & MCW infectious disease specialist and director of the Froedtert & MCW Travel Health Clinic, said.ae0fcc31ae342fd3a1346ebb1f342fcb And if you do experience this symptom, you need to get tested for COVID because it’s unlikely to be a sign of any other illness. “Even though with Omicron, it’s less likely that you’re going to lose your sense of smell or sense of taste, those are really specific for COVID-19,” El-Sayed told CNN. RELATED: For more up-to-date information, sign up for our daily newsletter. If you are having COVID-like symptoms or test positive for COVID, it’s important to know what you should do next. On Dec. 27, the CDC updated its recommendations for quarantining, changing some of its earlier timelines. Whether vaccinated or not, the agency says you should stay home and get tested if you develop any symptoms that have been attributed to COVID. If you’ve tested positive for the virus, you should quarantine for five days at home as well, regardless of vaccination status. “If you have no symptoms or your symptoms are resolving after 5 days, you can leave your house,” the CDC says, noting that you should continue wearing a mask around others for five additional days. The only exception is if one of your symptoms is a fever. “If you have a fever, continue to stay home until your fever resolves,” the CDC adds. RELATED: 70 Percent of Hospitalized Omicron Patients Have This in Common.