COVID, RSV, and influenza: Is it a case of viral overlap?

Three years into the pandemic, COVID-19 is still going strong, causing wave after wave as case numbers rise, fall, and then rise again. But last fall saw something new — or rather, something old: the return of the flu. In addition, the respiratory syncytial virus (RSV)—a virus that grabs a few headlines in normal years—caught on its own burst, creating a “triple pandemic.”

The sudden mutations in these ancient enemies were especially striking because influenza and RSV disappeared during the first two winters of pandemic. Even more surprising, a certain version of the flu might be Extinct During the early COVID pandemic. World Health Organization monitoring software It hasn’t definitively detected a B/Yamagata influenza strain since March 2020. “I don’t think anyone is going to stick their neck out and say it’s just gone,” says Richard Webby, a virologist at St. Jude Children’s Research Hospital in Memphis. But, he adds, “we hope it gets eliminated.” Webby says such an extinction would be an extremely rare event.

But then, the past few years have been very unusual times for human-virus relations, and lockdowns and masks have gone a long way toward preventing influenza and RSV from sneaking into a human’s nose. However, Webby believes another factor kept them apart during the coronavirus outbreak. 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 laboratory, in individual animals and people exposed to multiple viruses—but it can also occur across entire populations, if enough people become infected with one virus to disrupt the widespread flourishing of others. This results in waves of infection with individual viruses that take turns to dominate. “Looking back over the past two years, I’m pretty confident in saying that COVID can definitely prevent influenza and RSV,” says Webby.

This wouldn’t be the first time scientists have noticed such patterns. Back in 2009, for example, the virus of greatest fear was swine flu, which jumped from pigs to humans in the spring of that year. It seemed about to increase as fall came — but suddenly, in some parts of Europe, it stagnated. The rhinovirus, which is responsible for the common cold and likely spread by children returning to school, held center stage for several weeks before swine flu regained control. Then that flu strain Another typical fall hike for the RSV Up to two and a half months.

Enter running

There are a number of ways 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 grabs all the molecular doorknobs, virus B is out of luck.

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

But the best understood way of interfering has to do with a defense molecule called interferon Made from the cells of all animals with backbones (And maybe some invertebrates, too). In fact, viral interference is The reason why interferon gets its name Let’s start with When a cell senses a virus, any virus, it starts making an interferon. This in turn activates the file A large number of defense genes. Some of the products of these genes act within or at the cell’s borders, preventing additional viruses from entering and preventing viruses already present from multiplying or exiting the cell.

The cells secrete interferon into their surroundings, warning other cells to put their guard up. The upshot of all this: If a second virus appears, the cells will already have their defenses activated, and they may be able to shut down.