Respiratory syncytial virus – or RSV – was the first virus to strike much earlier than normal this season. It flooded pediatric hospitals in October and November instead of its usual peak from late December to mid-February, creating a severe shortage of pediatric beds.
Normally, the virus poses a particular risk to infants because it can inflame and clog the tiny airways in their lungs.
But this year, RSV hospitalized a much wider group of children, including older children with no underlying health conditions.
“I haven’t known the range of ages of the critically ill patients I’ve seen over the past few weeks,” said Dr. Chadi El Saleeby, a pediatric infectious disease specialist at Massachusetts General Hospital.
Many experts have suggested that RSV was worse this year due to an “immunity debt” or “immunity gap” resulting from years of social distancing and COVID precautions. Dr. Paul Offit, director of the Vaccine Education Center and professor of pediatrics at Children’s Hospital of Philadelphia, said much of the country is still masking up, social distancing and being winter cautious. last.
“That’s not true this year. People are back,” Offit said. “COVID no longer changes the way we live, work or play.”
With fewer cases of influenza and RSV in recent years, people haven’t received the “booster” of immunity that a typical yearly virus would create.
“Maybe that’s the same reason why the flu is definitely worse this year,” he said.
Other scientists doubt that mitigation measures have played a role in current trends. Michael Osterholm, director of the Minnesota Center of Excellence for Influenza Research and Surveillance, told a conference in Boston in November that the emergence of H1N1 in 2009 also disrupted normal patterns of RSV and flu the following winter. But at the time, people didn’t take mitigating measures.
“There was something going on with this virus that was impacting other respiratory pathogens,” Osterholm said.
Scientists also point out that RSV is not only more prevalent this year, but also appears to be more severe.
In the past, hospitals provided hydration, suction and some oxygen to patients diagnosed with RSV, but this year they had to provide more extensive respiratory support to more patients, El Saleeby said. .
Low population immunity may be part of the answer, but El Saleeby said infection with multiple viruses at once may also play a role. At MGH, several children tested positive not only for RSV, but also for enterovirus and influenza – which also arrived earlier in the season than normal.
“These breathing difficulties can be aggravated by the presence of several viruses at the same time,” El Saleeby said.
Ryan Gregory, a Canadian evolutionary biologist and professor at the University of Guelph in Ontario, agreed that there are likely multiple factors at play. He pointed to a recent small study published in the Lancet Respiratory Medicine that found that getting COVID during pregnancy could alter fetal lung development, resulting in children born with lower lung volume.
“That might explain why so many newborns are getting so sick,” Gregory said.
Although scientists have wondered if the recent RSV outbreak was caused by a new strain of the virus, early analyzes show that this does not appear to be the case. By examining the viral genomes of patients coming to MGH and some sites, researchers found that there were multiple versions of the existing virus in circulation, rather than a predominant new strain, according to a published preliminary analysis. on line last Friday.
However, more strains of RSV-A appear to be circulating this year, which is normally more severe than RSV-B, and this likely contributes to the increased severity of the recent outbreak, said Dr. diseases at MGH who co-directed the research.
Other scientists suggest that COVID infection could change how the human body responds to infections. Sometimes called “immunity robbery,” some have speculated that COVID could harm the immune system temporarily or in the longer term.
A controversial scientific theory, suggested by Anthony Leonardi, an immunologist and graduate student at the Johns Hopkins Bloomberg School of Public Health, postulates that COVID infection can deplete a key part of the immune system known as T cells, which contain much of the “memory” a person’s body has from previous infections. Multiple COVID infections could overactivate T cells, either aging them prematurely, engaging them so extensively that they accidentally cause organ damage, or taxing them for such a long time that they may become less effective against other viruses.
There are few clear answers, but Gregory of the University of Guelph said this is an urgent question for the scientific community to answer.
“If it’s just immunity [gap], if it’s just a numbers game and you get away with it, it’s going to be a bad year and we’re caught up, and next year should be good,” he said. “The consequences if it’s not that, if it’s immunity theft, are really serious. This year might not be the only bad year.
Jessica Bartlett can be contacted at email@example.com. Follow her on Twitter @ByJessBartlett.