RSV: Pandemic ‘immunity gap’ is probably behind surge in respiratory cases, scientists say


The measures that have helped protect us from Covid-19 over the past two and a half years — lockdowns, physical distancing, wearing face masks, washing hands — have also helped limit the spread of other viruses. As people go back to school and work and take off their masks, those viruses, including respiratory syncytial virus and the flu, are back in full force.

That “immune gap” of the past few years is behind this year’s “unprecedented” early surge in RSV infections, scientists say – and it has outstripped other seasonal respiratory viruses around the world.

“As long as we’ve had a record of RSV and other respiratory diseases in the United States, there have been these regular patterns of outbreaks,” said Rachel Baker, an epidemiologist and assistant professor at Brown University.

RSV emerges each year in the late fall/winter and these outbreaks are mostly in young children. Then it disappears again for the spring/summer months and reappears the following winter,” Baker said. “It’s very regular and predictable.”

Until it isn’t.

Cases of RSV in the United States began showing up in the spring and are now 60% higher than the peak week in 2021. A CNN analysis shows it’s probably an undercount.

Across the United States, the number of flu cases is increasing a little earlier than usual. A handful of schools have seen large absences, and doctors’ offices say they’re seeing more people getting sick with other respiratory viruses at times that don’t fit normal patterns.

There are similar unusual patterns in respiratory infections adenovirus, parainfluenza and rhinovirus in other countries as well.

Scientists think that the pandemic’s disparate actions had disparate effects.

“The scale of social change that has come with the Covid pandemic is unprecedented in modern times,” said Dr. Kevin Messaker, assistant professor in the Department of Pediatrics at Children’s Hospital Colorado.

Like Covid-19, RSV and the flu are spread through droplets released into the air when people cough or sneeze. Water droplets also linger on frequently touched surfaces such as doorknobs and light switches for hours.

So people washing hands and disinfecting surfaces, wearing masks and keeping their distance from others did more than stop the spread of the coronavirus.

“Those interventions, while they were great at limiting the spread of Covid-19, also did a good job of limiting the spread of other respiratory diseases like RSV and influenza,” Baker said.

Studies have shown a sudden drop in RSV cases and hospitalizations during the 2020 and 2021 seasons, with unusually mild flu seasons.

“It was really impressive,” Baker said.

But as Covid-19 vaccines and treatments became available, more people returned to school, worked and interacted without face masks. They also started sharing germs. Epidemic behavior has created an “immunity gap” or “immunity debt” that makes more people in the United States susceptible to diseases like RSV.

Children develop natural immunity to viruses when they are exposed to them. Most children catch RSV at some point before age 2, according to the US Centers for Disease Control and Prevention. Newborn babies receive some passive protection from their mothers who pass antibodies through breast milk.

But for several years, children born during the pandemic or people around them had no chance of catching RSV or other viruses. Their immunity was reduced or never developed. Therefore, when those young people and their parents associate with others, there is a high chance of them getting sick.

“Decreased exposure to endogenous viruses created an immune gap — a group of people who avoid infection and therefore lack pathogen-specific immunity to protect against future infection,” Messacar and Baker wrote in a commentary published this summer in the medical journal The Lancet.

They warned hospitals that they must remain flexible and prepare for unexpected respiratory illnesses because of this gap.

“We knew it was inevitable that these diseases would come back,” Messacar told CNN.

The commentary warned of an influx of infections, including older children who had not been exposed to the viruses, as well as newborns whose mothers were unable to pass on antibodies because they had not come into contact with these germs.

“Right now we’re seeing it spread pretty well,” Baker said. “It’s not just hitting kids that it usually hits with that first birth cohort. It also causes infections in older children.

“That’s how infectious diseases work,” she added. “Once you have more cases, they create more opportunities, and then you get this spike.”

Baker and Messacar don’t think this early-season pattern is permanent with RSV, but it may take some time to return to its more predictable cycle.

“Right now we’re in a little bit of a weird period, but I think in the next few years, we’ll start to see those normal outbreaks — well, depending on what happens with Covid,” Baker said. If the coronavirus is bad enough to require more lockdowns, it could throw off the seasonality of other viruses once again.

With viruses like the flu, more variables are involved, Messacar said.

There is no vaccine to prevent RSV, but there is for influenza, so if the flu vaccine is well-matched to the strain in circulation and enough people get it, the country could avoid the spike in cases it is now experiencing with RSV.

Scientists are working on an RSV vaccine, but it may not arrive in time to help this season.

In the meantime, there are a few things you can do to limit the spread of RSV, and they will be very familiar.

Wash your hands. Keep frequently used surfaces clean. Sneeze or cough into a tissue or elbow rather than your hands. Boost your immunity by getting enough sleep and eating a healthy diet. Wear a mask, especially when you are sick. Most importantly, if you are sick, stay home.

“All of these non-pharmaceutical interventions clearly work, and the more we can do to mitigate one of these viruses, the better,” Baker said.


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