Information regarding COVID-19 and vaccines are continually evolving, new details may be available since this content was developed. Please visit the CDC's website for the most up to date information.

Updated: 09/21/23 

Even years later, we’re continuing to learn new details about COVID-19. One area in particular that continues to confuse many people is how long it takes to develop symptoms after exposure (also known as the "incubation period") and how long a person stays contagious.

Our expert, Cristina Cicogna, M.D. an infectious disease specialist at Hackensack University Medical Center, breaks it down to clear up the confusion.

How quickly can you get COVID after exposure?

According to the Centers for Disease Control and Prevention (CDC), COVID has a long incubation period of up to 10 days. However, with newer strains, research has shown that the window of exposure time to experiencing symptoms is getting smaller and smaller. 

• An April 2023 study found that the incubation time for the Omicron variant BA.1 was only three days, compared to four days for the Delta variant.
• Another study looked at the evolving strains and found the incubation periods decreasing with each new strain – Apha with 5 days, Beta with 4.5 days, Delta with 4.41 days, and Omicron with 3.42 days. 

“Even with shorter incubation periods, the CDC still recommends you wear a mask for a full 10 days, starting from as soon as you discover you were exposed, even if you don’t have symptoms,” says Dr. Cicogna. “Start counting from day one, which is defined as the first full day after your last exposure.”

If you develop symptoms at any time, isolate yourself immediately and get tested.

When is the best time to test? 

According to CDC guidelines, if you have been exposed and continue to experience no symptoms, you should test at least five days after your last exposure. 

“When you discover you have been exposed, it might seem smart to get tested immediately,” Dr. Cicogna says. “However, getting tested too early may lead to a false-negative result. This can give a false sense of security and put others at risk.”

If the test result is negative, continue to take precautions until the 10-day mark. If you test positive, even if you aren’t symptomatic, you need to isolate for five days.

If you take a home antigen test, a negative test result doesn’t completely rule out infection. To be safe, consider serial testing to ensure you aren’t infectious—taking a second test 24–48 hours after your first negative result. 

How do I know if it’s reinfection or lingering positive results?

Reinfections can occur within 90 days. After a positive test result, you may continue to test positive for several weeks after the initial positive test. This makes it difficult to know if your new test indicates a new infection. “The best course of action would be to contact your health care provider regarding your results and individual circumstances,” says Dr. Cicogna.

“Everyone is different, so there isn’t a clear and easy answer regarding exposure and becoming sick. There are a lot of different scenarios and timelines to follow based on your exposure, if you are experiencing symptoms and whether you’ve tested positive or negative—and these timelines have changed numerous times over the past few years as the virus mutates and as scientists learn more,” says Dr. Cicogna. “If you are confused about what course of action to take if you’ve been exposed, have symptoms or have tested positive, contact your doctor for the most up-to-date recommendations to keep everyone safe.” 

Next Steps & Resources:

• Meet our source: Cristina Cicogna, M.D.
• To make an appointment with a primary care doctor near you, call 800-822-8905 or visit our website

The material provided through HealthU is intended to be used as general information only and should not replace the advice of your physician. Always consult your physician for individual care.