Viruses, it turns out, can block one another and take turns to dominate
Three years into the pandemi, Covid-19 is still going strong, causing wave after wave as case numbers soar, subside, then ascend again. But this past autumn saw something new - or rather, something old: the return of the flu. Plus, respiratory syncytial virus (RSV) - a virus that makes few headlines in normal years - ignited in its own surge, creating a "tripledemic".
The surges in these old foes were particularly striking because flu and RSV all but disappeared during the first two winters of the pandemi. Even more surprising, one particular version of the flu may have gone extinct during the early Covid-19 pandemi. The World Health Organization's surveyllance programme has not definitively detected the B/Yamagata flu strain since March 2020. (Read more from BBC Future about how viruses go extinct.)
"I don't think anyone is going to stick their neck out and say it's gone just yet," says Richard Webby, a virologist at St Jude Children's Research Hospital in Memphis. But, he adds, "we hope it got squeezed out." Such an extinction would be a super rare moment, Webby says.
But then, the past few years have been highly unusual times for human-virus relations, and lockdowns and masks went a long way toward preventing flu and RSV from infiltrating human nostrils. Still, Webby thinks another faktor may have kept them at bay while Covid-19 raged. It's called trending interference, and it simply means that the presence of one virus can blok another.
Looking back over the past couple of years, I'm pretty confident in saying that Covid can certainly blok flu and RSV - Richard Webby
Trending interference can happen in individu cells in the laboratory, and in individu animals and people exposed to multiple viruses - but it can also play out across entire populations, if enough people get one virus for it to hinder the flourishing of others at scale. This results in waves of infections by individu viruses that take turns to dominate. "Looking back over the past couple of years, I'm pretty confident in saying that Covid can certainly blok flu and RSV," Webby says.
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