A year after the World Health Organization first declared COVID-19 a pandemic, researchers are still working to understand the disease—and why some patients still experience symptoms months after being infected. According to a new study, many coronavirus "long-haulers" experienced only mild symptoms, or none at all, during the initial infection. The study analyzed the medical records of 1,407 people in California who tested positive but were never hospitalized. Researchers say there are likely many more undiagnosed cases of long COVID. "We know that some of the long-haul symptoms show up much later than two months," co-author Dr. Natalie Lambert tells the New York Times. "So there’s a potential for a wide range of long-haul symptoms that they’re not going to associate with COVID."
The study found that just over a quarter of patients, 59% of them women, reported symptoms more than 60 days after infection. Lambert also surveyed more than 5,000 people contacted through the Survivor Corps website for long-haulers, NBC News reports. She says that while more research is needed, early findings suggest that symptoms initially come in waves, with fever, chills, and gastrointestinal symptoms coming in the early stages, as with non-long haul patients, followed by heart and blood pressure issues about 15 days in, and symptoms like mouth sores and "COVID toes" arriving a week after that. After 60 days, researchers say, symptoms including coughs, muscle pain, headaches, and elevated heart rates arrive in clusters that can change from day to day. The study didn't look at "brain fog," which doctors say is also a common long-haul symptom. (Read more coronavirus stories.)