How Long Can Asymptomatic Coronavirus Carriers Infect Others?

This is what we know about COVID-19 disease spread from people who appear to be healthy.

One of the more puzzling aspects of the novel coronavirus has been the seemingly vast range of symptoms. For thousands of people around the world, COVID-19 has been severe or deadly. But for a large group of individuals, the illness has been practically invisible.

“There are some people who are truly infected, but they don’t get sick,” Stephen Gluckman, an infectious diseases physician at Penn Medicine and the medical director of Penn Global Medicine, told HuffPost.

These individuals are known as “asymptomatic carriers.” They often display no symptoms at all, or their symptoms are so insignificant they hardly notice them.

Anyone, regardless of age, can have an asymptomatic case of the virus. This phenomenon isn’t unique to COVID-19 either ― most infection symptoms exist on a spectrum from asymptomatic or mild to severe, Gluckman said.

It is not yet clear how many people are asymptomatic carriers of the disease. Nor is it clear how much they are contributing to the spread of the pandemic, though preliminary research suggests they likely play a significant role. Some estimates suggest 80% of coronavirus cases may be mild or asymptomatic. Experts also say we don’t have a full picture of the disease spread because many asymptomatic cases go unreported.

Similarly, it is not known how long those carriers may be contagious. That’s why it’s important to behave like we’ve already been exposed to coronavirus ― and could be carrying the disease ― and follow recommendations for preventing transmission, like social distancing.

“There is no easy, simple answer,” Faheem Younus, chief of infectious diseases at the University of Maryland Upper Chesapeake Health, told HuffPost.

The Centers for Disease Control and Prevention believes that people who have been infected with COVID-19 are at their most contagious at the peak of their symptoms. This means that the days people feel their worst ― that may include a cough or a fever ― are when they’re most likely to spread the virus.

But that does not mean it is the only time they are contagious. People can “shed” or emit the virus in the incubation period before they show symptoms, which is generally from two to 14 days after their initial exposure. One model found the median incubation period for COVID-19 was five days and that 98% of people who develop symptoms after an exposure do so in around 11 days.

Research also suggests that COVID-19 patients continue to shed the virus for days after their symptoms clear (this could explain why some people test positive for the virus even after they’re considered recovered). In general, individuals who are suspected of having COVID-19 are asked to remain in isolation for at least three days after they have recovered and for at least a week after their symptoms first appeared.

Younus pointed out that children are often asymptomatic carriers of COVID-19 and can pose a particular risk to those closest to them.

“The longer the duration, the closer the contact, the lower the host’s immunity, the higher the risk of catching the infection,” Younus said.

Gluckman said that he imagines researchers will have a better understanding of asymptomatic transmission of COVID-19 as time goes on, particularly as more studies come out of places like China, South Korea, Europe and the United States. But that kind of research relies on testing for the virus ― be it through swab testing when someone is sick or antibody testing after the fact ― which is the only way to capture silent cases of the illness.

“We will learn more about this novel coronavirus as more studies are conducted in a robust peer-reviewed fashion,” Younus echoed. “But that seems like a 2021 phenomena.”

For now, uncertainty about how many asymptomatic carriers there may be — and how long those carriers pose a risk to others they come into contact with — is why we should adhere to specific health and safety measures. That includes wearing face masks if it’s required in your area, washing your hands frequently, and limiting outings and your presence around crowds.

If you’re exposed to someone with coronavirus and you get infected, you could spread the virus long before you realize you’re sick (if you even realize it at all). And given that COVID-19 has spread throughout communities, you may not even know you’ve been exposed.

“People have to be vigilant about avoiding close contact with other individuals ... and not assuming that just because someone isn’t sick, they’re not carrying the virus,” Gluckman said. “We have to be very, very, very aggressive about self-isolating.”


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