The coronavirus can present itself with almost every symptom in the book, from vomiting to pink eye. But while you’ve probably been overanalyzing your cough and that sense of fatigue that comes over you at the end of a long day, the truth of the matter is your symptoms may not be the strongest indicator you’re sick—and that’s part of why COVID is so alarming. A new study from the University of Chicago’s Department of Ecology and Evolution has determined that the one thing the wide majority of COVID patients share is that their illness comes with no symptoms at all or symptoms that are so subtle, you’d hardly even notice them. Read on to find out more about how common asymptomatic cases really are, and for more on what’s to come with the pandemic, see why The U.K.’s Top Scientist Has a Chilling COVID Warning for Americans.
For the new study, which was published in the journal Proceedings of the National Academy of Sciences on Feb. 10, the researchers reviewed cases recorded in New York City from March to June. They concluded that only around 13 to 18 percent of COVID cases end up yielding significant symptoms, which means that around 80 percent of those who get infected with COVID are asymptomatic, or at least, experience such mild symptoms that they don’t realize they are infected.
“There are a lot of asymptomatic people—much larger than many studies have assumed,” study author Rahul Subramanian, a graduate researcher of epidemiology at the University of Chicago, told Insider. And for one subtle sign that could evade you, check out If You’re Over 65, You Could Be Missing This COVID Symptom, Study Says.
A lack of symptoms doesn’t mean you aren’t able to spread the virus, either. According to the study, asymptomatic cases and pre-symptomatic cases (those who are infected but have not yet started showing symptoms) “substantially drive community transmission.”
“We can tell that more that 50 percent of the transmission happening in the community is from people without symptoms—those who are asymptomatic and pre-symptomatic,” senior author Mercedes Pascual, PhD, the Louis Block Professor of Ecology and Evolution at the University of Chicago, said in a statement. And for more up-to-date COVID news delivered right to your inbox, sign up for our daily newsletter.
An asymptomatic case could also still affect you long-term. In fact, several studies have shown that long-term health issues arise in those who had COVID but had no symptoms. Eric J. Topol, MD, founder and director of Scripps Research Translational Institute, told The Wall Street Journal that at least four studies so far have analyzed the lung scans of asymptomatic individuals, finding that “half have significant abnormalities consistent with COVID pneumonia but without symptoms.” And a July study published in JAMA Cardiology discovered abnormal cardiac MRIs in both symptomatic and asymptomatic COVID patients, concluding that heart damage due to the virus is possible no matter how mild or severe your case is.
“There is a risk of internal hits to these people that they are unaware of,” Topol said. “When things happen slowly in a person, below the surface, you can end up with a chronic situation.” And for more on how the virus can progress, If You’ve Done This, You’re Twice as Likely to Develop Severe COVID.
The University of Chicago researchers say the study proves how much importance should be placed on testing non-symptomatic people, especially given the “ambiguity in recent Centers for Disease Control and Prevention (CDC) guidelines regarding the testing of asymptomatic individuals.” According to the CDC’s latest guidelines, most people without symptoms don’t need to get tested for COVID unless they have knowingly been in close contact with someone who is infected, which is within six feet for at least 15 minutes.
But study co-author Qixin He, PhD, now an assistant professor at Purdue University, cautions that the research proves “it’s crucial that everyone—including individuals who don’t show symptoms—adhere to public health guidelines, such as mask wearing and social distancing, and that mass testing is made easily accessible to all.” And for more from the nation’s leading health agency, If You’re Layering These Masks, the CDC Says to Stop Immediately.