Sick Season

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How Long Are You Contagious With These 6 Common Illnesses?

How long to keep to yourself if you catch one of these.

If it seems like your kids are sick all fall and winter, you’re not wrong. “The average kid gets about one viral illness that causes cold or flu-like symptoms a month. The average duration of those will be about two weeks,” says Dr. Valentine Rae Esposito, M.D., an attending physician in the division of general pediatrics at Boston Children’s Hospital. Look at that timeline, and it lines up: By the time kids recover from one illness… they’re just about to come down with another. That’s why figuring out exactly how long children are contagious with one specific virus or illness is tricky: They’re not always going from 100% healthy to sick and back.

Most childhood illnesses are the most contagious smack dab in the middle of them, roughly from day two to day four, which unfortunately often includes a window of time before symptoms crop up. “That’s why so many of these childhood illnesses just tear through day cares and schools,” says Dr. Katie Lockwood, M.D., a pediatrician at Children’s Hospital of Philadelphia (CHOP) Primary Care in Flourtown, Pennsylvania. “Sometimes kids don’t have many symptoms or don’t know that they’re sick yet, and they are actually contagious.”

Generally speaking, telltale signs that indicate kids are contagious with something are a fever of 100.4 Fahrenheit or higher, vomiting, or diarrhea within 24 hours.

“Fevers are a sign that the body is actively fighting an infection,” Esposito says. “Vomiting and diarrhea are also the body’s way of trying to get rid of something. Many different diseases can be spread through stool, so diarrhea can be a contagious component.”

Each illness, though, has a slightly different window of contagion. Here’s what you can expect in terms of a timeline from six common illnesses that could walk in the front door this winter per the Centers for Disease Control and Prevention (CDC) and pediatricians interviewed.


The CDC notes that you’re most likely infectious during the first five days of illness, which is when people should remain home; the group also recommends masking for 10 days. It is the go-source doctors rely on for guidelines regarding all things Covid-19.

One study in JAMA Pediatrics also found that the median time of infectivity was three days, with only about 18% of children still infectious on Day Five and 4% on Day 10.

If you have Covid symptoms and are wondering whether you isolate yourself and/or mask around others, Esposito recommends visiting the CDC’s site. “A lot of the guidelines are now based on the active symptoms you’re having,” says Esposito. “They have a great algorithm on their website for all of the different possibilities when it comes to exposures and symptoms, so that is definitely where I would send families.”


You’re most contagious with the flu in the first three to four days after the illness begins, but children may also be able to infect others even after five to seven days of symptoms.

“Some subtypes of flu can be contagious before symptoms start,” adds Dr. Krupa Playforth, M.D., a pediatrician and founder of The Pediatrician Mom.

Regarding your children, follow the golden rules of no fever and no vomiting or diarrhea within 24 hours to gauge contagiousness and whether they should be around others to prevent spreading the illness.


If your child is exposed to respiratory syncytial virus (RSV), they might not have symptoms for the first four to six days, explains Esposito. They’re usually contagious for three to eight days, but this window can be longer (weeks) in younger children and in those with compromised immune systems.

Remember, too, that pediatricians don’t always test for RSV because it doesn’t always change treatment plans, says Esposito, which are always focused on hydration respiratory status — aka how well a baby or child is breathing.


Your child is most likely to spread norovirus — a super contagious virus that causes vomiting and diarrhea — when they have symptoms, especially throwing up, and in the first few days when they start to feel better.

Playforth notes that norovirus can live on surfaces for weeks.

Studies also find that it’s possible to spread norovirus for two weeks after you’re feeling better, making handwashing and keeping surfaces clean paramount.

The Common Cold

No fever? No vomiting or diarrhea? Not RSV or Covid? Colds are most contagious during the first two to four days from transmission (when they were exposed to the illness).

If you’re trying to figure out whether or not it’s OK for your child to return to activities or school, look to see that symptoms are improving, that your child is eating and drinking fine, and that their energy levels match whatever the activity in question is, advises Lockwood.

“If you’re sending them back to school, you want to make sure that you feel like they have the energy and focus for a full day of learning and running around with their friends. If you think they don’t have the energy to make it through a full day, then they’re not ready to return.”

Strep Throat

If left untreated, strep throat can be serious, last a long time, and be contagious for about two weeks, says Lockwood.

Treating strep throat with antibiotics is an effective way to manage its contagious nature. “We typically let kids with strep throat go back to school after they've been treated with antibiotics for over 24 hours,” says Esposito. “So 24 hours from that first dose, they’re allowed to return to school.”

Preventing Spread

Of course, you can't keep your child home all winter. “Pediatricians want kids to be going to school and day care; we want them learning and growing and developing. We also want to keep our communities healthy,” says Esposito. “Look at cold and flu season like a team sport; we’re all just trying to stay healthy, and that involves everyone really making the effort to do that.”

There are ways to prevent the spread of common illnesses, including:

  • Immunizations for Covid-19, the flu, and respiratory syncytial virus (RSV)
  • Good handwashing — the “Happy Birthday” song twice at least and ideally up to the elbows (RSV, for one, can live on hands for 30 minutes)
  • Increasing ventilation in your home by opening some windows
  • Cleaning high-contact surfaces like doorknobs, phones, and toys frequently

The Bottom Line(s)

Worries about common illnesses are normal — and it makes sense to want to keep your children and those around you healthy. While you can take preventative measures to slow the spread of illnesses, sometimes knowing what to look out for — and remembering a few key points — can also help you mitigate passing sicknesses inadvertently to others and quell fears and anxieties.

  • Most children get about one common illness, such as a cold or flu, a month throughout the fall and winter.
  • Many of these conditions are contagious for a few days to a few weeks, with each one having slightly different contagion criteria.
  • Many can be managed and mitigated with at-home remedies.
  • When it comes to illnesses in children, keep an eye on when symptoms start, if they are eating and drinking or how many wet diapers they have a day, fever, and breathing. If you see any rapid breathing or “pulling” in of the ribs or around the neck or nostril flaring, these are signs that your child is having a harder time breathing, which means they need medical assistance. Never hesitate to contact your pediatrician for advice.


  • Dr. Valentine Rae Esposito, M.D., an attending physician in the division of general pediatrics at Boston Children’s Hospital
  • Dr. Katie Lockwood, M.D., a pediatrician at Children’s Hospital of Philadelphia (CHOP) Primary Care in Flourtown, Pennsylvania
  • Dr. Krupa Playforth, M.D., a pediatrician and founder of The Pediatrician Mom