COVID, RSV and the flu: A case of viral interference?

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Three years after the pandemic, COVID-19 is still going strong, causing wave after wave as case numbers rise, fall, then climb again. But last fall 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—fired on its rise, creating a “tripledemia.”

The increases in these old enemies were particularly surprising because influenza and RSV disappeared during the first two winters of the pandemic. Even more surprising, a particular version of the flu may have disappeared during the early COVID pandemic. The World Health Organization’s surveillance program hasn’t definitively detected the B/Yamagata strain since March 2020. “I don’t think anyone is going to stick their neck out and say it’s gone yet,” says Richard Webby, a virologist in St. Jewish Children’s Research Hospital in Memphis. But, he adds, “we hope it has been squeezed out.” Such an extinction would be a super rare event, Webby says.

But then, the last few years have been very unusual times for human-virus relations, and masks and masks went a long way toward preventing flu and RSV from getting into human noses. However, Webby thinks another factor may have kept them at bay while COVID was raging. It’s called viral interference and it simply means that the presence of one virus can block another.

Viral interference can occur in individual cells in the lab, and in individual animals and humans that are exposed to multiple viruses—but it can also occur in entire populations if enough people get one virus that it prevents others from flourishing. in the stairs . This results in waves of infection from individual viruses that dominate in turn. “Looking back over the last couple of years, I’m very confident in saying that COVID can certainly block flu and RSV,” says Webby.

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It would not be the first time that scientists have observed such patterns. In 2009, for example, the virus to fear was swine flu, which had jumped from pigs to humans in the spring of that year. It looked set to grow with the arrival of autumn – but suddenly, in some parts of Europe, it stalled. The rhinovirus, responsible for the common cold and likely spread by children returning to school, took the spotlight for several weeks before swine flu regained dominance. That flu strain then delayed the typical fall surge of RSV by up to two and a half months.

Interference with work

There are a number of ways that interference can occur in the body. One occurs when two viruses use the same molecule to enter host cells. If virus A gets there first and gets caught by all those molecular gloves, then virus B is out of luck.

Another type of interference can occur if two viruses compete for the same resources inside the cell, such as the machinery to make new viral proteins or the means to escape that cell to infect others. “Think of it as a race between two viruses,” says Webby.

But the best-understood method of intervention involves a protective molecule called interferon that is made by the cells of all vertebrates (and possibly some invertebrates). Indeed, viral interference is why interferon got its name in the first place. When a cell senses a virus, any virus, it starts producing interferon. And this, in turn, activates a host of protective genes. Some of the products of these genes work inside the cell or at its borders, where they prevent additional viruses from entering and block viruses already present from replicating or leaving the cell.

Cells secrete interferon into their environment, warning other cells to maintain their defenses. The result of all this: If a second virus comes along, the cells have already activated their defenses and they may be able to shut it down.