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 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 COVID-19?
Viruses are constantly changing, which sometimes leads to new strains called “variants.” Different COVID-19 variants can have different incubation periods.
When researchers set out to learn the incubation period for the original strain of the coronavirus, they studied dozens of confirmed cases 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 Omicron Variant?
Omicron is now the most dominant strain of coronavirus in the U.S., and its incubation period may be shorter than those of previous variants. Research is just beginning. But some scientists who've studied Omicron and doctors who've treated patients with it suggest the right number might be around 3 days.
Some early research suggests Omicron may be more contagious than the Delta variant. But health experts are still looking into how sick it can make people and how well vaccines and treatments work against it.
They expect vaccines and booster shots to help protect people from serious illness, hospitalization, and death. If you’re fully vaccinated and you get a breakthrough infection of Omicron, you’re less likely to become seriously ill than an unvaccinated person.
What Is the Incubation Period for the Delta Variant?
The Delta variant, which evolved from previous strains of COVID-19, was once the most dominant type of coronavirus in the U.S. Research shows it spreads faster and has a shorter incubation period than the SARS-CoV-2 variants that came before it.
Delta’s incubation is around 4 days, compared to the 5.6 days for earlier strains. This means that if you get infected with the Delta strain, your symptoms may show up much faster. Your body will also shed the virus earlier.
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 earlier variants. In fact, one study from China showed that in infections caused by Delta, the viral load was 1,000 times more than that of previous coronavirus strains.
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.
It's possible that, because of its shorter incubation period, you may become contagious more quickly if you have the Omicron variant. But we need more research on this.
If I Have COVID-19, How Long Am I Contagious?
According to the CDC, if you have mild to moderate COVID-19, you may be contagious for 10 days from the first day you noticed symptoms.
If you were severely affected or critically ill from COVID-19, you may stay infectious for up to 20 days from the start of your symptoms.
A large-scale review of 113 studies of COVID-19 from 17 countries found that if you have COVID-19, your infectiousness is highest 1 day before the start of your symptoms and begins to wane about a week later for most people. The review included several COVID-19 variants that emerged before Omicron, including Delta.
Studies have also found that the Omicron variant has a shorter incubation period, compared to other variants. For the Omicron variant, the incubation period is 2 to 4 days.
Can I Get or Spread COVID-19 During or After the Vaccination Process?
When you get a COVID-19 vaccine, it teaches your immune system to recognize the virus as a foreign element and fight it. Studies show that COVID-19 vaccines can greatly reduce your chances of getting infected with the virus. But if you do catch it after you’re vaccinated, 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 if you are:
- Fully vaccinated with possible COVID symptoms
- Unvaccinated or not fully vaccinated
If you’re unvaccinated or are more than 6 months away from your second mRNA dose (or more than 2 months after the J&J vaccine) and haven’t yet had your booster shot, the CDC recommends you:
- Isolate for 5 days.
- Follow strict mask use for 5 more days.
But if the 5-day quarantine isn’t possible for you, the CDC suggests you wear a well-fitted mask around other people for 10 days after exposure.
If you’ve gotten your vaccination and booster shot, you don’t need to quarantine after coming into contact with a positive COVID-19 case. But you should wear a mask for 10 days after exposure.
If you’ve been exposed in any case, the best option would also include a COVID-19 test on the fifth day after exposure. If you start to have symptoms, you should quarantine until you get a negative test that shows your symptoms weren’t caused by COVID-19.
Still, after you leave quarantine, you should continue to monitor yourself for any symptoms.
What if I Get Sick or Test Positive While in Quarantine?
Take extra safety measures if you think or know you have COVID, or if you test positive for the virus but don't have symptoms. Isolate yourself from other people in your home. Choose a “sick room” or separate area to stay in, and use a different bathroom if possible.
The CDC has shortened its recommended isolation time for people with COVID-19 to 5 days if you don’t have symptoms. After this period, they suggest you wear a mask around others for 5 more days.
If you have a fever, you should continue your isolation until it goes away.