CHICAGO (CBS) — The novel coronavirus is not the only virus in the headlines this week.

Another one that is most common in babies under 6 months old failed to materialize in most kids during our year of wearing masks and keeping kids out of school. But now, hospitals are seeing a doubling of kids with respiratory syncytial virus, or RSV.

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As CBS 2’s Chris Tye reported, the phenomenon has caught some medical professionals off guard.

RSV is a virus every young child gets. A total of 70 percent of children get it in their first year of life, and by age 3, they will all have had it.

But no school and masks everywhere kept RSV from popping up for a year, and now it is showing up in double speed and filling up hospitals.

“We didn’t see any in the last 18 months. It was astounding how few children we were seeing sick with respiratory viruses,” said Dr. Allison Bartlett, who specializes in pediatric infectious diseases at UChicago Medicine. “But now, we’re paying for it on the back end a little bit.”

RSV infects the lungs and breathing passages. Healthy people typically experience mild, cold-like symptoms including cough, congestion, and fever.

But the virus can be serious among infants and the elderly – leading to as many as 14,500 deaths a year.

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For the very young, it can damage and inflame the small airwaves of the lungs and block air from moving.

The surge in cases began in the southern part of the U.S. in recent months, but it has come north quick.

“The loosening of who we are hanging out with, and who we’re hanging out with without without masks, and kids back in school and ready for them to be normal in the spring is what ended us up here,” Bartlett said.

In Illinois, RSV cases were flatlined almost all of last year. But in April, as mask rules relaxed and schools were back in person, cases spiked.

“We have two years’ worth of children who’ve never had their first infection of RSV, and so we’re playing catchup now,” Bartlett said. “Our hospitals are full.”

In peak RSV season – October to March – Medicaid covers a treatment to decrease hospitalization risk by half for those without full health coverage. Illinois, unlike some neighboring states, is not offering it in these off-peak months – leaving some of the most vulnerable at higher risk.

“It’s definitely very concerning and atypical this time of year,” Bartlett said. “It’s certainly the wrong time of year for this to be happening.”

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Dr. Bartlett said the State of Illinois is looking at expanding those treatments to tamp down RSV hospitalization risks to Medicaid patients, but no decision has been made yet.