COVID-19 Incubation Period: Average Number of Days After Exposure

Strains of the SARS-CoV-2 virus that causes COVID-19 circulating in 2023 typically took about three days from exposure to showing symptoms. This incubation period is shorter than previous strains of the virus. It may take up to a week before an at-home antigen test shows positive.

This article will review the the incubation periods of various SARS-CoV-2 virus variants, from Alpha to Omicron, after exposure and how long it typically takes to get a positive test. It will also discuss multiple reasons times may differ from person to person, including vaccination and booster status, general health, and if you’ve had COVID-19 before.

COVID-19 Incubation Period: How Soon After Exposure Can Symptoms Start?

Terminology relating to viral illness varies. Here are a few key terms used in this article to clarify what what they mean:

• The virus’s incubation period is how long it takes for symptoms to start after exposure. 
• The time after exposure before you get a positive test on an over-the-counter antigen test can be longer or shorter than the incubation period before symptoms start.
• The quarantine period is a requirement by your work, school, or local government to stay away from others after you’ve been exposed to a virus or have a positive test.
• The virus’s contagiousness is how easily it spreads between people, which is influenced by your immune status and general health. A virus can be transmitted before and after you have symptoms, so a virus’s contagious period can be longer than its incubation or symptomatic periods.
• The virus’s transmission route is how it spreads between people—through the air or from surfaces. You can transmit the virus to another person during the virus’s contagious period.

According to the Centers for Disease Control and Prevention (CDC), COVID-19 symptoms may appear anywhere from two to 14 days after exposure to the virus.

A review of studies conducted from 2020 to March 2022 indicated an average incubation period for COVID-19 at six to seven days, ranging from 1.8 to 18.87 days. The average incubation period shortened as new variants circulated, with Omicron at an average of 3.42 days.

Variants and Strains to Know 

As COVID-19 is transmitted from person to person, it mutates (changes genetically) along the way. These mutations can change the virus enough that it may develop into a new strain.

New strains, or variants, can have changes in common symptoms, how easily they spread, and how long they take to cause illness.

Many variants have circulated since 2020. A variant of concern (defined by the CDC) passes between people faster, is more virulent (has greater potential to cause disease), has shown resistance to a vaccine or immunity from a previous infection, or doesn’t show up on current tests.

The average incubation periods of the main variants from the 2022 review study were:

• Alpha variant: 5.0 days
• Beta variant: 4.50 days
• Delta variant: 4.41 days
• Omicron variant: 3.42 days

The 2023 COVID strains, including Omicron and its subvariants, appear to be more transmissible because of their shorter incubation period. Studies on Omicron indicate a shorter incubation period with an average of three to four days after exposure before symptoms show up.

The variant circling in most areas in late 2023 was Omicron-5, or EG.5, first reported in February 2023. Incubation period data is not yet available for the EG.5 subvariant. Still, experts say it seems to be behaving similarly to past iterations of Omicron. The incubation period of Omicron-5 is about three to four days. 

COVID-19 Symptoms 

The symptoms of a COVID-19 infection can vary from asymptomatic (no symptoms) to mild or severe.

If you've been vaccinated, boosted (received a booster shot), or have had COVID-19 in the past, your symptoms are likely to be less severe. But if you've had a change in your immune system (for example, pregnancy or a new medication or illness), your symptoms may be more severe than previous infections. 

Many symptoms are very similar to those of other upper respiratory viruses, including the common cold, influenza, and respiratory syncytial virus (RSV), which have similar seasonality (their transmission often peaks in the fall and winter). If you have symptoms, over-the-counter tests can help determine whether you have COVID-19. 

An Omicron infection's first signs and symptoms include sore throat, dry cough, and fever. The most commonly reported COVID-19 symptoms are:

• Fever or chills
• Sore throat
• Cough
• Shortness of breath or difficulty breathing
• Fatigue
• Muscle or body aches
• Headache
• Congestion, runny nose, or sneezing
• Nausea or vomiting
• Diarrhea

COVID-19 Incubation Period: How Soon After Exposure Will a Test Be Positive?

You should start testing for COVID-19 after waiting at least five days after potential exposure to someone who is sick. Test again one to two days later. Then, test again another couple of days later. You should plan to take three tests within five days to make sure you’re in the clear.

Getting a positive test on an at-home COVID-19 antigen test may take a week or longer after exposure or symptom onset. A lab-based PCR (polymerase chain reaction) test would show a positive result much earlier. You should wear a mask when around other people for 10 days after a potential exposure.

Common Q&As About COVID Incubation Period

When you've had a potential COVID exposure or have been in contact with someone who is sick, you're sure to have a lot of questions. Here are the answers to some common questions people have about COVID incubation periods.

How Does COVID Incubation Period Compare to Other Viruses?

COVID seems to have a more extended incubation period than other common respiratory illnesses. Different viral incubation periods include:

• Other coronaviruses: 3.2 days
• Influenza A: Around 1.5 days
• Parainfluenza: 2.6 days
• RSV: 4.4 days
• Rhinovirus (causes the common cold): 1.4 days

Can I Spread COVID During the Incubation Period?

Presymptomatic and asymptomatic transmission of COVID-19 has been a significant factor in the pandemic's spread. This virus seems to spread quickly before it causes symptoms. If you’ve been exposed to COVID, it’s possible you can spread it, even if you don’t feel sick—and potentially even if you never feel sick.

This contagious period for COVID lasts from before you start feeling sick until your at-home antigen test turns negative.

Does the Incubation Period Change Based on Vaccination Status? 

If vaccinated and boosted against COVID-19, you’re more likely to have a milder infection. But studies suggest the virus’s incubation period will remain the same.

Does the Incubation Period Change Based on Age?

Some studies have suggested that the average incubation period in people 60 and older may be longer, around seven to eight days, than in the general population. Studies have also shown that children under age 18 may have an incubation period of 8 to 9 days.

Should I Call a Healthcare Provider If I Get a Positive COVID Test?

If you’re generally healthy and are current with your COVID-19 vaccinations, there’s no need to seek medical care after a positive COVID test. 

Call a healthcare provider if you’re at high risk for severe infection, for example, if you have a weakened immune system, are over 65, or haven’t been vaccinated. They can prescribe Paxlovid (nirmatrelvir/ritonavir), a prescription oral antiviral pill for a COVID-19 infection. It can help with recovery and decrease the risk of severe complications.

If you see any of these emergency warning signs, seek immediate medical help:

• You’re having trouble breathing.
• You have pain or pressure in the chest that doesn’t go away.
• You’re experiencing confusion.
• You’re having a hard time waking up or staying awake.
• Your skin, lips, or nail beds turn pale, gray, or blue.

How Long Should I Isolate If I Test Positive for COVID?

You'll want to let your workplace or school know if you've been exposed to COVID and get a positive test result. They may want you to isolate and stay home for a certain amount of time.

You should avoid being around others while testing positive for COVID. That includes other people in your house. Try to stay in one room, away from other people. Wear a mask if you will be around others. Stay home to avoid transmitting the virus. If you need to go out of the house, wear a mask.

Day zero is the day you first had symptoms or, if you had no symptoms, the day you first tested positive for COVID-19. CDC guidance for isolation is as follows:

• You may end isolation on day five if you have had no symptoms or your symptoms are improving and you have had no fever for 24 hours without taking a medication that reduces fever.
• If your symptoms are not improving, isolate until they are improving and you have no fever for 24 hours without taking a fever-reducing medication.
• If you have moderate symptoms such as difficulty breathing, isolate through day 10.
• If you were hospitalized or have a weakened immune system, isolate through day 10 or when cleared to do so by a healthcare provider.

For anyone after isolation, continue to wear a mask when around others (at home and in public) until at least day 11.

Summary

The incubation periods of COVID-19 variants vary. Generally, the incubation period is getting shorter. Symptoms of recent strains like Omicron typically show up about three to four days after exposure. The newer Omicron-5 variant is similar to the original Omicron strain. 

Getting a positive COVID test at home may take a week to 10 days. Regular testing after potential exposure can minimize your risk of spreading the virus. 

The first COVID symptoms are typically a dry cough, sore throat, and fever. These are similar to other respiratory viruses that spread in the fall and winter. The COVID incubation period tends to be slightly longer than some of these other viruses. 

Studies suggest that COVID-19 vaccine and booster status don't change the incubation period, but factors like age might. Older people and children may have a more extended COVID incubation period.