How Long Are You Contagious After Catching a Virus?

If there’s one positive that came out of the pandemic, it could be our heightened awareness of how viruses, particularly the respiratory kind, can spread from one person to another. The super-sick person who insists on “toughing it out” and coming into the office or school (and getting several other people sick as a result) has fortunately fallen out of favor.

At this point it’s clear that no one wants to be the bearer of bad germs, but there's no consensus on when to return to civilization and what precautions, such as masking, may be necessary.

Keep reading to find out how long you’re contagious if you have a cold, the flu, COVID-19, or RSV, and how factors like vaccination status, medications, or symptom severity play a role.

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.

“Colds are caused by many different viruses, and rhinovirus (which has many types) is the most common cause,” he says. Other common cold viruses include adenoviruses and coronaviruses.

That’s why you can get multiple colds in one season — because they can be caused by different viruses or strains, explains Dr. Winslow.

“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 onset of symptoms,” says Winslow.

For people with upper respiratory symptoms, Winslow recommends wearing a mask for about five or six days after your symptoms begin, in order to protect other people. By that time, the amount of the virus you’re shedding is a lot less and you’re unlikely to pass the cold on to someone else, he says.

Symptoms of the flu can range from mild to severe, and include:

• Fever
• Chills
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle aches
• Headaches
• Fatigue
• Vomiting and diarrhea (though the GI symptoms are more common in children)

Flu is mostly spread through the air by tiny droplets generated when infected people cough, sneeze, or talk, which can then go on to land in the mouths or noses of others. It can also be spread by contact with objects — if a person touches something with the flu virus on it and then touches their nose or mouth — though that’s less common.

As with a cold, you can shed the flu virus and infect other people up to 24 hours prior to onset of symptoms, says Winslow. “You’re most contagious the first day or two after the onset of symptoms,” he says.

By day three or four, you may still have a lot of symptoms as a result of your immune system being activated, but the amount of virus that you're shedding is lower, he says. “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,” says Winslow.

The flu shot can reduce your chances of getting the flu. If you do get the flu even after getting immunized, it’s less likely that you’ll become severely ill.

There isn’t enough evidence to show that already being vaccinated against the flu influences how long you’ll be contagious if you do still get the virus, says Winslow.

But a medication such as Tamiflu (oseltamivir) taken within the first 48 hours after onset of symptoms probably does make 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.

Symptoms of RSV infection usually include runny nose, decrease in appetite, coughing, sneezing, fever, and wheezing.

The RSV vaccine is relatively new, and it isn’t known whether it can affect how long you are contagious, says Winslow.

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

COVID-19 symptoms can 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

The virus spreads via droplets and very small particles exhaled by people with COVID-19. Others can then catch the virus if these particles are breathed in or land on people’s eyes, noses, or mouth. More rarely, virus particles can land on surfaces and be spread that way.

“Research has confirmed that you can be contagious up to 24 hours prior to onset of symptoms and then you are most contagious one to two days after the onset of symptoms,” says Winslow.

• Practice good hygiene. Wash hands frequently, cover coughing and sneezing, and sanitize frequently touched surfaces.
• Aim for clean air. Open windows, use air purifiers, or gather outdoors.
• Wear a mask. The best mask is the safest one you can wear comfortably for an extended period of time.
• Distance yourself physically. There is no “safe” distance, but putting space between you and others can lower the risk of spreading infection.

If you do have symptoms, you should stay at home until your symptoms begin to improve and you don’t have a fever for 24 hours (without taking fever-reducing medication). You should follow the above precautions for the following five days to avoid spreading the illness to others.

It has been shown that symptom severity generally correlates with the viral load, and so it makes sense that if you have some preexisting immunity from the vaccine, you’re less likely to be shedding the virus, says Winslow.

Antiviral drugs (such as Paxlovid) taken shortly after symptoms start may reduce viral shedding, he says.

• How long you’re contagious when you get a viral respiratory infection can depend on several factors, including what kind of illness you have and whether you’ve been vaccinated.
• With cold, flu, RSV, and COVID-19, people tend to be most contagious a day or so before symptoms appear and then a day or two after the onset of symptoms — although people with RSV may remain highly contagious for the duration of their symptoms.
• If you have symptomatic COVID-19, you should stay home until your symptoms begin to improve and you go 24 hours without a fever (without the use of fever-reducing medication).