With flu season underway and new variants of Covid in the mix, medical professionals have warned of a “triple threat” as these illnesses coincide with a wave of another common virus: respiratory syncytial virus, or RSV.

Dr. David Cornfield is a pediatrician at Stanford Medicine engaged in patient care and research and a professor in pediatric pulmonary medicine. (He also sits on J.’s board.) He spoke with J. about the risks of this respiratory virus that hits children the hardest, why it’s making a big comeback — and when to worry, or not.

The interview has been condensed and edited.

J.: What is respiratory syncytial virus?

Dr. David Cornfield: RSV is an exceedingly common childhood infection. It was discovered in 1956, and since 1957 it’s made pretty much an annual appearance.

We know that it is ubiquitous; about half of all children get RSV by the time they’re 1 year old. And by the time kids are 3 years of age, virtually every child on the planet has had RSV.

We know, too, that for most children, it’s a fairly innocuous cold that doesn’t need medical attention. So RSV, in general, is not something that should be viewed with a great deal of anxiety and concern — because it’s a cold, essentially.

So why are we hearing about it so much this year?

There’s little question that this year RSV has come earlier, and it is affecting more children. And it seems to be marginally more severe, although that’s not altogether clear.

We know that with social distancing and masking and kids not being in school for the past several years, there’s been a real decrease in normal transmission of respiratory viruses during the winter months. With a return to a bit more normalcy, kids are now interacting in a way that is facilitating the transfer of viral particles.

By 3 years of age, virtually every child on the planet has had RSV.

And there are now several years of children who have no immunity to RSV. Instead of having just one year or even six months of children who have not seen the infection, we now have three years of children who have not seen the infection, all of whom are now susceptible and many of whom are being exposed to the virus. And of those who are exposed, some number are more significantly affected and need medical attention.

What makes someone likely to be more affected?

RSV for the most part is an innocuous infection. However, there are some populations of people who really are at risk for problems from RSV. There are some infants and kids with preexisting conditions — premature infants with congenital heart disease, kids with chronic lung disease — that all are more susceptible to having a severe bout of RSV, or having more severe symptoms with RSV.

And it’s also the case that RSV can be a problem for the elderly, as well, who generally haven’t seen the infection for many years and often don’t have as robust immune systems. So protecting both young infants and vulnerable adults is really prudent in the context of RSV. That said, I want to emphasize that the overwhelming vast majority of children who get RSV do very well and never need to seek further medical attention.

Is the larger number of kids needing attention for RSV posing a strain on medical professionals?

Absolutely, hospitals that care for children across the Bay are working at capacity. Care givers, nurses, respiratory therapists, pharmacists, doctors and all other care team members are working long and hard to deliver care to these children.

Since there’s no vaccine for RSV, what are the best protocols for not spreading it?

Good handwashing, masking when you’re around people who have any sort of signs of infection, staying home and not going out when you yourself or your family have signs of infection are all prudent ways of proceeding.