Coronavirus Incubation Period

What Is an Incubation Period?

The incubation period is the number of days between when you’re infected with something and when you might see symptoms. Health care professionals and government officials use this number to decide how long people need to stay away from others during an outbreak. It’s different for every condition.

If you’ve been around someone who has the new coronavirus that causes COVID-19, you’re at risk, too. That means you need to stay home until you know you’re in the clear. Health professionals call this self-quarantine. But when will you know whether you have the disease? The answer depends on the incubation period.

What Is the Incubation Period for the New Coronavirus?

To learn the incubation period for the coronavirus, researchers studied dozens of confirmed cases of COVID-19 reported between Jan. 4 and Feb. 24, 2020. These cases included only people who knew that they’d been around someone who was sick.

On average, symptoms showed up in the newly infected person about 5.6 days after contact. Rarely, symptoms appeared as soon as 2 days after exposure. Most people with symptoms had them by day 12. And most of the other ill people were sick by day 14. In rare cases, symptoms can show up after 14 days. Researchers think this happens with about 1 out of every 100 people.

Some people may have the coronavirus and never show symptoms. Others may not know that they have it because their symptoms are very mild. Current studies might not include the mildest cases, and the incubation period could be different for these.

What Is the Incubation Period for the Delta Variant?

The Delta variant, which evolved from previous strains of COVID-19, is currently the most dominant type of coronavirus in the U.S. The mutation allows the virus to produce a higher load of viral particles in the body. This makes the Delta variant more than 2 times as contagious as other variants. In fact, one study from China showed that in infections caused by the variant, the viral load was 1,000 times more than that of previous coronavirus strains.

Research also shows that the Delta variant spreads faster and has a shorter incubation period than previous SARS-CoV-2 variants. Delta’s incubation is around 4 days, compared to the 5.6 days in other strains. This means that if you become infected with the Delta strain, your symptoms may show up much faster. Your body will also shed the virus earlier.

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When Is the Coronavirus the Most Contagious?

Researchers estimate that people who get infected with the coronavirus can spread it to others 2 to 3 days before symptoms start and are most contagious 1 to 2 days before they feel sick.

Can I Get or Spread COVID-19 During or After the Vaccination Process?

When you get the COVID-19 vaccine, it teaches your immune system to recognize the virus as a foreign element and fight it. Studies show that the COVID-19 vaccine can greatly reduce your chances of getting infected with the virus. But if you do catch it after you’re vaccinated -- in what is being called a “breakthrough” infection -- the vaccine will still protect you from getting as seriously ill or needing hospitalization.

It’s important to note that you’re not optimally protected until 2 weeks after you get your second dose of a two-shot vaccine. That’s because it takes around 2 weeks for your body to build protection against the SARS-CoV-2 virus. And because the incubation period is shorter than the wait time between doses, it’s possible to catch COVID-19 before or just after your vaccination, since your body has not had enough time to build immunity. If this happens, the CDC recommends waiting until you’ve fully recovered to get the vaccine.

How Long Should I Quarantine After I’ve Been Exposed to the Coronavirus?

The CDC says that if you might have come into contact with the virus and have no symptoms, you should self-monitor. This means watching for signs such as fever, cough, and shortness of breath. Stay out of crowded places, keep at least 6 feet away from other people, and wear a cloth face mask when you have to go out.

If you traveled recently or know that you came into contact with someone who has COVID-19, you should self-quarantine. Stay home for 14 days. It’s very rare for symptoms to show up after that much time. Check your temperature twice a day, and watch for other symptoms. Stay away from other people, especially those who are at high risk of serious illness because of their age or another medical condition.

If 14 days of isolation creates a hardship, the CDC advises you may be able to leave quarantine:

  • After day 10 without testing
  • After day 7 after receiving a negative test result

Still, after you leave quarantine, you should continue to monitor yourself for any symptoms.

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What Should I Do If I’m Fully Vaccinated and I’ve Been Exposed to the Coronavirus?

If you’re fully vaccinated and you’ve come in contact with someone infected with COVID-19, the CDC recommends that you:

  • Get tested 3-5 days after exposure. Do this even if you don’t have any symptoms.
  • Wear a mask indoors in public for 14 days after exposure or until your COVID-19 test result is negative.

WebMD Medical Reference Reviewed by Neha Pathak, MD on September 30, 2021

Sources

SOURCES:

Nature Medicine: “Temporal dynamics in viral shedding and transmissibility of COVID-19.”

CDC: “Coronavirus Disease 2019 (COVID-19): Social Distancing, Quarantine, and Isolation," “Quick-Learn Lessons: Incubation Period,” “Key Things to Know About COVID-19 Vaccines,” “Delta Variant: What We Know About the Science,” “Quarantine and Isolation,” “Frequently Asked Questions about COVID-19 Vaccination.”

Annals of Internal Medicine: “The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application.”

Sutter Health: “Delta Variant? Experts Answer Questions on Latest Outbreak.”

MedRxiv: “Viral infection and transmission in a large, well-traced outbreak caused by the SARS-CoV-2 Delta variant.”

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