RELATED: If You Notice This on Your Face, It Could Be an Omicron Symptom. If you get infected with COVID these days, you’re almost certainly dealing with the Omicron variant. According to the Centers for Disease Control and Prevention (CDC), this variant is currently estimated to account for more than 99 percent of new cases in the U.S. The Washington State Department of Health reported on Jan. 26 that 60 percent of Omicron patients reported having a headache, making it one of the most-common symptoms of the variant.ae0fcc31ae342fd3a1346ebb1f342fcb “Even though headaches are a less well-known symptom of COVID-19, they are one of the earliest signs of the disease and more common than the ‘classic’ symptoms of cough, fever and loss of smell,” the researchers at Zoe COVID Study explain on their website. And with Omicron, these classic COVID symptoms are appearing less often, while headache is appearing more frequently. “You shouldn’t be waiting for the three classic symptoms,” Tim Spector, lead scientist on the Zoe Covid Study App, confirmed in a statement. Headaches have been associated with COVID for some time now, and the Omicron variant is no different. But head pain isn’t always a sign of coronavirus infection, so researchers have been looking for a way to tell the difference between a COVID headache and a non-COVID one. According to the Zoe COVID Study App, doctors have pinpointed five factors that tend to be present when someone is dealing with this symptom because of the coronavirus. A COVID headache usually has three distinct factors in terms of how it feels: it’s moderately to severely painful, it occurs across both sides of the head rather than in one area, and it is pulsing, pressing, or stabbing. But there are also two more characteristics you should watch out for. If you have a headache because you have Omicron, it is also likely to last for more than three days and be resistant to regular painkillers. RELATED: For more health news sent right to your inbox, sign up for our daily newsletter. It isn’t surprising that COVID is causing this type of head pain. “Many respiratory viruses—including COVID—cause headaches,” Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, told Prevention. William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine told the magazine that with COVID, “the general thought is that your body is experiencing an inflammatory reaction as it fights off the virus,” and a headache is part of that response. But doctors say there also might be a reason as to why this symptom seems to be occurring more often with the Omicron variant. This version of the virus appears to be more focused on the upper respiratory tract—which includes your sinuses—than previous variants, Thomas Russo, MD, a professor and chief of infectious disease at the University at Buffalo in New York, told Prevention. “[And] a headache commonly occurs with inflammation of the sinuses,” he explained, adding that combined with the stress of being infected with COVID, it’s “highly plausible” that people with Omicron would develop a headache. If you’ve gotten your shots, you might want to be more vigilant in watching out for this Omicron symptom. Maya N. Clark-Cutaia, PhD, a professor at the New York University Meyers College of Nursing, told The New York Times that vaccinated patients who get infected with Omicron tend to complain of headaches, as well as body aches and fever, more often than unvaccinated patients. Adalja told Prevention that this might also be because symptoms of Omicron are milder in people who are fully vaccinated, which might make less severe symptoms like a headache more noticeable. On the other hand, unvaccinated individuals are more likely to have some of the more classic, flu-like symptoms when infected with Omicron. According to Clark-Cutaia, people who have not been vaccinated are still often experiencing shortness of breath and a cough with this variant. RELATED: These 4 New COVID Symptoms Could Mean You Have Omicron, Doctors Warn.