With holidays approaching in the United States, health experts warned that COVID-19 isn't defeated yet and seasonal influenza could launch an attack, despite the federal government's endeavor to vaccinate more Americans against the coronavirus.

"It's a good time to reflect on why it's important to get vaccinated. But go out there and enjoy Halloween as well as the other holidays that will be coming up," Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN on Sunday.

However, as the conditions are improving and the sense of normalcy is expanding, Fauci still alerted the nation that the fight against the pandemic is not over.

"We still have around 68 million people who are eligible to be vaccinated that have not yet gotten vaccinated," he said.

Experts are warning that there could be what they call a "twindemic" of COVID-19 and flu this coming winter, reported national broadcaster CBS on Monday. Last week, The Washington Post reported that U.S. health officials are urging Americans to get their flu shots, warning that the flu season that didn't materialize when most of society was shut down last year could come roaring back and strain hospitals in the months ahead.

On Monday, data from the U.S. Centers for Disease Control and Prevention (CDC) showed that 65.3 percent of the whole U.S. population have received at least one dose of COVID-19 vaccine, 56.4 percent fully vaccinated, of whom 4.2 percent have received booster shots.

To offer booster doses to a wider range of Americans, a U.S. Food and Drug Administration (FDA) advisory panel of vaccine experts plan to meet on Thursday and Friday to discuss booster doses of the Johnson & Johnson and Moderna coronavirus vaccines.

"Federal officials have become increasingly worried, in particular about the more than 15 million Americans who received the Johnson & Johnson vaccine, which is less effective than the others," reported The New York Times.

So far, regulators have authorized booster shots only for certain adults who received the Pfizer-BioNTech vaccine.

The expert committee will also hear a presentation on Friday from scientists on the effectiveness of mixing different brands of vaccines.

On Monday, drugmaker Merck asked the FDA to authorize its pill against COVID-19 in what would add an entirely new and easy-to-use weapon to the world's arsenal against the pandemic.

If cleared by the agency, a decision that could come in a matter of weeks, it would be the first pill shown to treat COVID-19.

(With input from Xinhua News Agency)