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What Is Asymptomatic COVID-19 and Are You Contagious?

Studies suggest 1 in 5 people infected with the coronavirus never develop symptoms

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The emergence of COVID-19 and its slow integration into our daily lives has impacted everybody. But that impact hasn’t been the same across the board. One reason? The physical experience of being sick with COVID-19 can vary wildly from person to person. Contracting COVID-19 is deadly for some, while others don’t get so much as a sniffle. How exactly is that possible?

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We’re learning more about COVID-19 every day. And there’s so much information out there that it can be hard to keep up. We asked infectious disease specialist Donald Dumford, MD, to bring us up to date on asymptomatic COVID-19. He details the ongoing research on the topic and explains how we can use what we know to navigate our “new normal” in a smart, safe way.

What does asymptomatic COVID-19 mean?

Simply put, the word “asymptomatic” means being sick without having symptoms. No fever, no cough, no body aches, no fatigue. Nothing. Your body’s actively battling a disease — and in some cases spreading it — without you even realizing you’re unwell.

It’s called being an “asymptomatic carrier.” Asymptomatic carriage isn’t something that happens with all diseases, but it does happen with COVID-19. And it happens quite a bit. Dr. Dumford says it’s one of the reasons the virus proved impossible to contain — and why it transitioned from an isolated outbreak to a global pandemic so quickly.

Asymptomatic vs. pre-symptomatic COVID-19

Dr. Dumford notes that it’s common to confuse asymptomatic COVID-19 with pre-symptomatic COVID-19, so let’s clarify these terms.

As we mentioned, an asymptomatic person goes through the whole course of their illness without developing symptoms. They may never even realize they were sick. The term “pre-symptomatic” meanwhile, refers to what’s called an incubation period. That’s the time between getting infected and showing symptoms of an illness.

All viruses, including COVID-19, have an incubation period. In many cases, it’s when the virus is most contagious. While they are two different things, being pre-symptomatic and being asymptomatic are both tricky from a disease prevention standpoint because in both cases, a person can pass the virus on to other people without realizing they’re doing it.

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How common is it?

Asymptomatic COVID-19 is quite common. Scientists think that at least 20% of all people infected with COVID-19 never have symptoms. Meanwhile, because COVID-19 reinfection is common — and many of us have established some immunity to the virus — it’s not unusual to experience both symptomatic and asymptomatic COVID-19 infections over the course of one’s life.

At this stage in the pandemic, whether or not having COVID-19 will make you feel sick is, at least partially, a game of chance. But there’s a growing body of evidence indicating that some of us are playing with loaded dice.

Studies indicate that children and adolescents may be more likely to have an asymptomatic infection than adults. Research also suggests that a lack of COVID-19 symptoms may sometimes be determined by genetics. That would make sense because we already know that some people are genetically predisposed to developing critical cases of COVID-19 pneumonia. These two branches of COVID-19-related research may one day help us limit the severity of symptoms in people who are prone to severe complications.

Are you still contagious?

Dr. Dumford explains that not having symptoms of COVID-19 doesn’t mean you can’t infect other people. And the people you infect have the same risk of having symptoms that you did.

In other words, the virus you’re passing on isn’t different. What’s different is how your body responds.

“Given that so many people with COVID show minimal to no symptoms, the possibility of exposure is present virtually every day,” Dr. Dumford says. “That makes preventive measures all the more important, especially if you or somebody you love is vulnerable to severe complications from COVID.”

What should you do if you test positive?

The U.S. Centers for Disease Control and Prevention (CDC) announced significant changes in COVID-19 isolation guidance on March 1, 2024. Their new policy says that isolation should be determined on the basis of clinical symptoms. That means you can end your isolation as soon as:

  • You’ve been fever-free for over 24 hours, without taking medication.
  • Any other symptoms that you have are mild and improving.

You see where this is going: People with asymptomatic COVID-19 infections now aren’t required to isolate at all. It’s still encouraged to wear a well-fitting mask for the five days after coming out of isolation. If you don’t have to isolate at all, Dr. Dumford says you should still strongly consider masking in public for five days after you’re diagnosed.

Asymptomatic COVID-19 cases have always slipped through the net to a certain extent, even at the height of the pandemic. But in the past, many people had to submit to regular testing to attend work or school. Required testing is much rarer nowadays — and many people are no longer able to isolate for five days without facing professional or academic consequences. The pandemic isn’t over, but it sometimes feels like it is.

What does all this mean in practical terms?

  • If you have symptomatic COVID-19: Follow the CDC recommendations regarding isolation and masking.
  • If you’ve been exposed: You could have asymptomatic or pre-symptomatic COVID-19. Strongly consider masking around others for the next five to 10 days. If symptoms arise during that time, then discuss testing and isolation with your provider.
  • If you test positive: Whether or not you have to isolate, Dr. Dumford recommends you wear a mask around other people until you’re well again. After all, there are still many people who are immunocompromised, chronically ill or otherwise vulnerable to severe COVID-19 complications. In fact, somewhere between 1,500 and 2,500 people still die in the U.S. every week as a result of COVID-19.
  • If you’re high-risk for COVID-19 complications: Operate under the assumption — as you already do for contagious respiratory infections like the flu or respiratory syncytial virus (RSV) — that people around you may be infected. Dr. Dumford says that might be a reason to wear masks and avoid large indoor gatherings. But ultimately, we all have to decide for ourselves how much risk we consider acceptable.
  • Stay up to date on your vaccines. If you’ve recently had COVID-19, symptomatic or not, you have some natural immunity to the virus. But it’s not enough, especially given how many variants are circulating around the world at any given time. And keep in mind: Being asymptomatic once isn’t a guarantee that you won’t feel sick if you contract COVID-19 in the future. “Getting vaccinated and boosted is your best protection against infection and severe illness,” Dr. Dumford states.

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Long-term symptoms may still develop

There’s one other thing to be aware of: While it’s rare, some people with asymptomatic COVID-19 do go on to develop long COVID. In other words, they develop symptoms days, weeks or months after the virus resolves. And those symptoms continue for months or, in some cases, years.

The bottom line

Approximately 20% of individuals infected with COVID-19 are asymptomatic. That means they don’t have any symptoms and may never even know they were sick. That’s a problem from a public health standpoint because the person who had COVID-19 is still contagious and can unknowingly spread the virus to other people. It’s also reason #418 that staying up to date on your COVID-19 vaccines is so important.

If you know that you have an asymptomatic case of COVID-19, be sure that you wear a mask and practice social distancing if you’re going to be around other people. Isolation guidelines are changing as the virus becomes part of our everyday lives, but your responsibility to protect others from infection isn’t.

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