Dr. Anthony Fauci has a sober warning for Americans: Don't be surprised if a new, more dangerous Covid variant emerges this upcoming winter.

"We should anticipate that we very well may get another variant that would emerge, that would elude the immune response that we've gotten from infection and/or from vaccination," Fauci said at an event with the USC Annenberg Center for Health Journalism this week.

Statistically, pandemic trends like hospitalizations and deaths are currently down nationwide: The seven-day moving average of new Covid deaths in the U.S. is 323 as of Wednesday, for example. That's far lower than the country's 1,000 to 2,500 in February and March, according to data from the Centers for Disease Control and Prevention.

But Fauci urged Americans not to let their guard down because there's always a "risk of uptick" in the winter months. "It looks like we're going in the right direction," he said, adding: "However, I think it would be a bit cavalier to all of a sudden say, 'We're completely through with [the pandemic].'"

Fauci pointed to the summer of 2021, when the U.S. saw similarly low pandemic trends, only for the omicron variant to emerge and cause a record-breaking surge in cases last winter. Since then, multiple subvariants of omicron have spread and become dominant in the U.S.

That includes BA.5, which currently makes up 81.3% of all cases circulating, according to CDC data. BA.5 and its predecessor, BA.4, are three times less sensitive to antibodies from the original Covid vaccines than even the original omicron strain, research suggests.

"We shouldn't be surprised" if another new, more transmissible variant emerges this winter, Fauci said. Emerging research suggests that some new subvariants, including one called BA.4.6, appear to evade immunity even more effectively than BA.5 — though it's unclear whether any of them will overtake BA.5 as the country's dominant Covid strain.

That makes getting a new omicron-specific Covid booster all the more crucial, Fauci noted. All Americans ages 12 and older are eligible for one, if they've completed their primary Covid vaccine series. Roughly a third of U.S. adults say they've already gotten a new booster or intend to "as soon as possible," according to a Kaiser Family Foundation poll last week.

"We're encouraging people, particularly as we're now in the fall season, to get that particular updated vaccine, which fortunately for us is directed at the major circulating variant," Fauci said.

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