How Long Are You Contagious After Catching a Virus?

Even when you start feeling better, you may still be able to spread the virus. Taking extra precautions, such as masking and practicing good hygiene, can help reduce the risk of infecting others.

The common cold is a mild upper respiratory illness that’s relatively contagious, says Dean Winslow, MD, a professor of medicine and an infectious disease physician at Stanford Medicine in California.

“You can actually be contagious for up to a day or so prior to onset of your symptoms, and then usually you're most contagious for about 24 to 48 hours after,” says Dr. Winslow.

For people with upper respiratory symptoms, Winslow recommends wearing a mask for about five or six days after symptoms begin. After that time, you’re shedding much less of the virus and are unlikely to pass the cold on to someone else, he says.

As with a cold, you can spread the flu up to 24 hours before onset of symptoms and for five to seven days after getting sick.

“Even though it’s less likely to spread by that point, you are still potentially contagious. To be safe, I would recommend that people wear a mask pretty much the whole time they have upper respiratory symptoms,” Winslow says.

Young children and people with weakened immune systems may stay contagious for longer.

Flu symptoms range from mild to severe and can include:

• Fever or chills (not everyone with flu will have a fever)
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle aches
• Headaches
• Fatigue
• Vomiting and diarrhea (though GI symptoms are more common in children than in adults)

Do Flu Shots or Antivirals Shorten Your Contagious Window?

Taking an antiviral such as oseltamivir (Tamiflu) within the first 48 hours of symptom onset probably makes you less contagious, says Winslow. “It definitely reduces the duration of symptoms and also very likely has at least a modest effect on reducing viral shedding because it is an antiviral,” he says.

COVID-19 is very contagious. “The way the virus has evolved is that it tends to become more contagious and cause less disease, which is a common strategy that most pathogens take in terms of their evolution,” Winslow says.

The virus spreads via droplets and very small particles exhaled by people with COVID-19. Others can then catch the virus by breathing in these particles or when the particles land in their eyes, nose, or mouth. More rarely, the virus particles can spread through surfaces.

COVID-19 symptoms range from mild to severe and can include:

• Fever
• Chills
• Cough
• Shortness of breath
• Fatigue
• Muscle or body aches
• Headache
• Loss of taste or smell
• Sore throat
• Congestion or runny nose
• Nausea
• Vomiting and diarrhea

Vaccination and antiviral treatment may shorten how long you're contagious. Symptom severity generally correlates with the amount of virus in your body, so people with some immunity from vaccination are likely shedding less virus, says Winslow. Taking antivirals such as nirmatrelvir and ritonavir (Paxlovid) shortly after symptoms start may also reduce viral shedding, he adds.

After the first few days of symptoms, the amount of virus you shed drops dramatically — unless your immune system is compromised, says Winslow. Infants and people with weakened immune systems can stay contagious for four weeks or longer, even if they stop showing symptoms.

RSV is a highly contagious virus that inflames the respiratory tract and usually causes mild, cold-like symptoms, such as runny nose, decreased appetite, coughing, sneezing, fever, and wheezing. Symptoms typically appear four to six days after infection. It can be hard to tell the difference between a cold and RSV, though RSV usually produces more mucus.

RSV can spread through droplets released into the air by coughing or sneezing, direct contact such as kissing, or touching a contaminated object like a doorknob and then touching your mouth, nose, or eyes.

It’s unclear whether the RSV vaccine affects how long you are contagious, says Winslow.

For the next five days when you go back to your normal routine, take extra precautions when you’re around others:

• Aim for cleaner air. Bring in fresh air by opening windows and using air purifiers, or gather outdoors whenever possible.
• Practice good hygiene. Wash your hands often with soap and water, cover your coughs and sneezes with a tissue or your elbow, and clean frequently touched surfaces.
• Wear a mask. A well-fitted mask can act as a filter to reduce the number of germs you breathe in or out.

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• Keep your physical distance. There’s no single number that defines a “safe” distance, but putting more space between you and others can lower the risk of spreading the virus.