You may have heard about pediatric hospital wards being overwhelmed by cases of RSV . While RSV is not a new virus and usually causes only mild symptoms, there are a couple of factors at play that make this year unique when it comes to RSV infections.

Heres what you need to know.

What is RSV and who is at risk?

Respiratory syncytial virus, or RSV, is a common respiratory virus that causes the same symptoms as a cold, such as a runny nose. Symptoms are usually mild and go away after a week or two in adults and children, but babies can develop bronchiolitis inflammation of the small airways in the lungs and require more intensive treatment.

Almost all children have had RSV by age 2 years and will be reinfected throughout their life, Dr. Ruth Kanthula , a pediatric infectious disease specialist with MedStar Health, told HuffPost. Subsequent infections, she said, are milder than the first one.

According to the Centers for Disease Control and Prevention , RSV is the No. 1 cause of bronchiolitis and pneumonia (infection of the lungs) in babies under one year of age. RSV can also cause more serious illness in seniors or people who are immunocompromised.

A lot of what puts babies particularly those under 6 months of age at risk for bronchiolitis is simply their size. Their small airways increase the likelihood of breathing difficulties.

The chest wall is more elastic, Dr. Janine Zee-Cheng , a pediatrician practicing in Indiana, told HuffPost. A babys lungs are less likely when they get inflamed to be able to sort of hold themselves open like an adult, she continued.

The CDC estimates that 58,000 children under the age of 5 are hospitalized with RSV every year, most of them infants or children with other health conditions.

What is different about the RSV infections doctors and hospitals are seeing right now?

The main differences are the timing of the RSV infections and the end of pandemic protections like masking and social distancing.

We typically dont see high numbers of RSV until later in the season, said Kanthula, who noted cases usually peak in February.

This year the virus has been circulating since spring and summer, which is very unusual, she added.

Now that children are back in school without masking and social distancing, kids are being exposed to lots of viruses, including RSV, in a way that they havent been for the past couple of years.

We are seeing more [RSV] now in kids who are older than usually they would be, as well as more cases overall, said Zee-Cheng.

Its possible that high case numbers now are a result of low case numbers during the pandemic when social distancing and masking were in effect. Kids who would have usually gotten their first RSV infection as babies or toddlers may only be getting it now because they werent exposed during infancy.

Zee-Cheng is one of the authors of a study published in the journal Chest showing a sharp drop in the number of children admitted to the pediatric intensive care unit with bronchiolitis and pneumonia during April-June of 2020.

Bronchiolitis had an 80% drop after the school closures went into effect, she said.

This was part of a general trend in fewer PICU admissions during this time.

Pediatricians like Zee-Cheng are also noting a current surge in respiratory illness among children who are not hospitalized, although we dont know if this is from RSV or other viruses.

I have gotten lots of calls about kids who are having persistent cough for two weeks, she said. Kids are wheezing who have never wheezed before. Theyre having these coughs that just last and last.

What are the symptoms of RSV?

RSV presents much like any other respiratory virus, including COVID-19 or the flu, as a runny nose, cough or decrease in appetite. Some children also have a fever, though Kanthula notes that she sees this less often with RSV than other viruses.

In a very young infant, irritability or lack of appetite might be the only initial symptoms.

Symptoms can get worse a few days into the illness, with a cough progressing into wheezing.

When should parents call the doctor?

Parents should contact their pediatrician right away if their child shows signs of trouble breathing. If a child is having to work harder than usual to breathe, you may notice their stomach moving.

You can see the ribs moving up and down, the belly working really hard, said Zee-Cheng.

You might notice childrens nostrils flaring open as they breathe in.

Babies struggling to breathe may also make a grunting sound with each breath, which parents could mistake for fussiness.

If you notice any of these signs of respiratory distress in your child, you should consult a doctor right away.

How can parents protect their children from infection?

There is a monoclonal antibody treatment (palivizumab) available to protect children who are most vulnerable to RSV, such as premature infants or those with heart defects. But there is not yet a vaccine for RSV, so the best way to prevent infection is to use the general precautions that we are all familiar with: hand-washing, cleaning frequently touched surfaces (like doorknobs) and keeping a safe distance from anyone who is sick.

Its possible to have more than one respiratory virus at the same time, which Kanthula said can be associated with more severe symptoms, so make sure that everyone in your household is up to date with COVID-19 and flu vaccines.

The data on pediatric hospitalizations prove that masking and social distancing worked to prevent kids from getting all kinds of respiratory viruses, not just COVID-19.

If youre the parent of a young infant, its reasonable to take these same precautions now. You can ask people to wash their hands and wear masks when visiting the baby, and isolate the baby when an older child is sick.

My general advice for people with newborns is to avoid taking them places, said Zee-Cheng. This is not the only time that your friends and family are going to get to see the baby.