In the shadow of the past year’s coronavirus surge came a less noticeable, but more positive infectious-disease trend: Influenza and other common viruses have nearly disappeared.

The flu is circulating at such low levels that officials know of only one child in the United States who has died of it this flu season, a striking deviation from the dozens of pediatric deaths in other recent years.

This season’s death toll is a marked decline from the 2019-2020 flu season, when the Centers for Disease Control and Prevention reported 195 children died of the flu. While influenza typically keeps circulating in March and April, experts say a combination of coronavirus precautions and existing immunity has so far nearly eradicated infection levels and, by extension, deaths.

“I think that that obliteration of the flu epidemic, which was seen globally, tells us that the way that influenza is transmitted from one person to another might really have been impacted by the use of masks, more than anything else,” said Flor Munoz, a member of the American Academy of Pediatrics’ infectious-diseases committee.

Influenza spreads reliably each fall and winter, although with different dominant strains and at varying levels. But this year’s coronavirus pandemic has caused many people to keep their distance from others, avoid travel and work from home, stalling flu transmission.

Widespread mask-wearing may be particularly helpful because face coverings limit the spread of the droplets that carry influenza, Munoz said. A dominant pathogen, like the coronavirus that causes covid-19, can also crowd out other viruses by conferring partial immunity to them. Combined with the flu vaccine and existing immunity, those factors have made flu circulation nearly negligible.

The result has been that only about 0.1 percent of flu tests are coming back positive, compared with 20 to 30 percent at this time in other years, said Lynnette Brammer, who leads the CDC’s domestic influenza surveillance team. Adults are also experiencing a dramatic drop in influenza deaths, with about 450 so far this season, compared with roughly 22,000 last year.

The current trend is unlikely to hold. Influenza is expected to come roaring back next fall and winter if most coronavirus restrictions have lifted by then, experts warn. Because children commonly spread the flu, reopened schools and day-care centers may contribute significantly to the rebound.

That prediction is not just theoretical. Recent data from several countries, including Cambodia, Laos and Bangladesh, showed the flu resurging as coronavirus restrictions were lifted and students returned to schools, Brammer said.

But flu infections and deaths could stay low next season if mask-wearing and social distancing remain common, either because of the coronavirus or because people choose to apply the same measures to influenza prevention.

“I think this has clearly shown that masking, distancing, hand-washing — all these things clearly work,” said Aaron Milstone, an epidemiologist and professor of pediatrics at Johns Hopkins University. “So I think the question will be, how much appetite do people have for all that to prevent influenza, instead of just covid.”

Some experts speculate that next flu season might be particularly harsh. Among other reasons, the near nonexistence of influenza this year has complicated scientists’ efforts to figure out which strain was dominant and might stay prevalent.

Andrea Kovacs, chief of the division of pediatric infectious diseases at the University of Southern California, said it’s hard to predict which strains to develop vaccines for next year without data for the current year.

“They may not guess the right strains to make the vaccine against,” Kovacs said.

It also isn’t too late for the flu to surge in the current season if coronavirus restrictions are relaxed. A change in human behavior could make flu cases rise in April and May, when they’re usually decreasing, Brammer warned.

“We could have a maybe small, but late, flu season,” she said. “Just really hard to say.”