One of the more puzzling aspects of Covid-19 has been the seemingly vast range of symptoms.

For thousands of people around the world, the virus has been deadly. But for an unquantified group of individuals (at least so far), 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 “asymptomatic carriers” ― who have no symptoms at all (or whose symptoms are so mild they go unnoticed) ― are not unique to Covid-19.

“When we get infections, there is often a spectrum from very sick to modestly sick to not sick at all,” Gluckman said. 

Unfortunately, that represents the full extent of what health experts know with any certainty about asymptomatic carriers of Covid-19 at this time. 

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 epidemic, though preliminary research suggests they might play a significant role.  Similarly, it is not known how long those carriers may be contagious.

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

The best we can all do right now is act like we’re already a carrier of the virus and follow current recommendations for preventing transmission.

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 recent 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 within 11½ days. 

Research also suggests that Covid-19 patients continue to shed the virus for days after their symptoms clear. 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 told HuffPost that he imagines researchers will have a better understanding of asymptomatic transmission of Covid-19 in the next month or so, if not sooner, 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, 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 social distancing measures. 

If you’re exposed to someone with coronavirus and you get infected, you could spread the virus long before you realise you’re sick (if you even realise 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.”

This story has been updated to include more information about COVID-19 infections and will continue to be updated as more knowledge about the virus becomes available.