Doctors are beginning to notice Covid-19 cases that look more like a very bad cold, especially in areas of the country where the highly contagious delta variant is quickly spreading.
While shortness of breath and other lung issues remain among the most worrisome Covid-19 symptoms, it appears upper respiratory complaints — marked by congestion, a runny nose and headache — may be increasing.
"We've seen a number of folks with cold-like symptoms," said Dr. Robert Hopkins Jr., an internist at the University of Arkansas for Medical Sciences in Little Rock.
The potential shift in symptoms is not to say that the illness should be brushed off as just a cold. Respiratory droplets emitted from coughs and sneezes can infect other, more vulnerable, people. And cases that start off mild can worsen and become more serious.
"Covid can present in different ways," said Dr. Russell Vinik, chief medical operations officer at the University of Utah Health in Salt Lake City. "If you think you have a cold, you're infectious, and whether that's Covid or a cold, you should consider getting a test."
Vinik has also seen more people coming in with cold-like symptoms. And previously typical Covid-19 symptoms such as loss of taste and smell are not as commonly reported anymore, he said.
Both Hopkins and Vinik said their patients tend to be unvaccinated and skew younger than earlier in the pandemic.
It is not clear why common cold symptoms are increasingly reported in Covid-19 cases, though some experts suspect it could be due to the delta variant, which now accounts for about 20 percent of new cases in the U.S. Arkansas and Utah, where Hopkins and Vinik are respectively based, have some of the highest rates of delta cases in the country, according to the Centers for Disease Control and Prevention.
Indeed, in the United Kingdom, where delta is implicated in more than 95 percent of new cases, researchers say the most common symptoms of Covid-19 are now that of a bad cold: headache, sore throat, runny nose and fever.
"What we've been seeing in the last month is very much a change in the symptoms," said Tim Spector, a professor of epidemiology at King's College London.
Spector heads a project called the ZOE Covid Study, an app where users report symptoms, vaccination status and other demographic information daily. More than 4 million people in the U.K. have signed on, as well as about 300,000 people in the U.S.
"We get a picture of where things are happening in real time," Spector said. "We also get to hear about the commonest symptoms in different times of year and in different locations."
Spector's research finds that earlier symptoms, such as shortness of breath, persistent cough and loss of smell, "have dropped out of the top five" of the most common Covid-19 symptoms.
The CDC has long included classic "common cold" symptoms of congestion and a runny nose on its list potential Covid-19 symptoms. A spokesperson told NBC News the agency has no immediate plan to change symptom guidance.
Still, physicians in the U.S. are paying attention to what's happening in the U.K., which is "two to three months ahead of us," Vinik said.
Dr. Andy Dunn, a family physician and chief of staff at Wyoming Medical Center in Casper, agreed, adding that what is happening now in the U.K. could predict Covid-19 cases later this summer and into fall.
It's also possible the shift in Covid-19 symptoms has nothing to with the delta variant. Now that most older adults have received the Covid-19 vaccine, new cases are skewing toward younger, mostly unvaccinated, adults. Younger people have generally been spared the worst of Covid-19.
"Now that we have vaccinated all of those older people, you take their symptoms out of the mix," said Alasdair Munro, a senior clinical research fellow in pediatric infectious diseases at the National Institute for Health Research in the U.K.
"People who would get those milder symptoms normally are now a much bigger proportion of everyone who gets infected," Munro said.
Dunn estimates that three-quarters of his Covid-19 patients now are under age 50. He is also seeing an uptick in congestion associated with the virus.
Most of Dunn's sickest Covid-19 patients are unvaccinated. Wyoming is one of the states with the lowest vaccination rates in the country; just over 30 percent of residents are fully vaccinated.
Dunn said the combination of the low vaccination rate and societal unmasking has led to "huge breeding grounds for more variants to evolve and to really grab ahold of a community that could have wiped this out with vaccines."
Don't think you're immune to Covid just because you're vaccinated.
But even those who have been vaccinated are not entirely immune to Covid-19. While highly effective, the vaccines do not prevent 100 percent of infections. Breakthrough cases — infections in people who are fully vaccinated — can occur.
"If you've been vaccinated and you have symptoms, don't discount them. You could still get Covid," Vinik, of the University of Utah Health, said.
"Don't think you're immune to Covid just because you're vaccinated," he warned.
That means even among the vaccinated crowd, a stuffed-up nose, sore throat, slight fever or fatigue may warrant a Covid-19 test.
"Is it just a cold? Or is it Covid? We're not doing enough testing to have a good idea of how much Covid is circulating in our communities," Hopkins, of the University of Arkansas Medical Center, said.
Spector, of the U.K.'s ZOE project, had more pointed advice.
"If you're not sure it's a cold, I would assume it could be Covid," he said.