BETHESDA -- With rising numbers of COVID-19 cases predicted this winter, U.S. President Joe Biden on Thursday appealed for Americans to get their boosters and get behind his plan to tackle the new omicron variant through wider availability of vaccines and shots, but without new major restrictions on daily life.

Biden wants to require private insurers to cover the cost of at-home COVID-19 tests and he is tightening testing requirements for people entering the United States, regardless of their vaccination status. While some other countries are closing their borders or reinstituting lockdowns, the president said he would not at this time impose additional clampdowns beyond his recommendation that Americans wear masks indoors in public settings.

"Experts say the COVID-19 cases will continue to rise in the weeks ahead this winter, so we need to be ready," Biden said during a visit to the National Institutes of Health in suburban Maryland after a briefing with scientific advisers.

He said his new strategy "doesn't include shutdowns and lockdowns," and he hoped for bipartisan backing.

"My plan I'm announcing today pulls no punches in the fight against COVID-19, and it's a plan that I think should unite us," he Biden said.

Legal challenges have held up Biden's vaccination-or-testing requirement for workers at larger employers, and that's led the president to urge businesses to impose their own mandates so companies can stay open without outbreaks.

His administration has come to view widespread adoption of booster shots as its most effective tool for combating COVID-19 this winter. Medical experts say boosters provide enhanced and more enduring protection, including against new variants.

Much remains unknown about the omicron variant, such as whether it is more contagious, makes people more seriously ill and can thwart the vaccines. Officials said Thursday that a second case of the variant had been confirmed in the United States.

About 100 million Americans are eligible for boosters under current U.S. policy, with more becoming eligible every day. Officials believe that persuading the vaccinated to get another dose will be easier than vaccinating the roughly 43 million adult Americans who haven't gotten a shot.

"Go get your booster now," Biden said.

Seniors are in the population most vulnerable to the virus, and the Centers for Medicare & Medicaid Services will send a notice to all 63 million Medicare beneficiaries encouraging them to get booster doses, the White House said. The AARP will work with the administration on education campaigns for seniors.

So far about 42 million Americans, about half of them seniors, have received a booster dose. The Centers for Disease Control and Prevention this week broadened its booster dose recommendation to cover all Americans at least age 18, starting six months after their second dose of the mRNA vaccines from Pfizer or Moderna.

Biden said the CDC is developing new guidance for schools in an effort to reduce or eliminate current quarantine requirements for those not fully vaccinated and exposed to the virus. That could include "test-to-stay" policies, in which those considered close contacts can continue to go to school but wear masks and undergo serial testing, in an effort to minimize learning loss and disruption.

The rule that private insurers cover at-home testing is being drafted, and details remain to be worked out, officials said.

People insured by Medicare and Medicaid would not be eligible, but the White House said as many as 150 million people with private insurance would see easier and cheaper access to the at-home tests. The administration said it is making 50 million COVID-19 tests free for older people and other vulnerable groups for pickup at senior centers and community sites.

Beginning next week, Biden said, all travelers to the U.S., regardless of nationality or vaccination status, will need to provide proof of a negative COVID-19 test within one day of boarding flights. That compares with three days now for those who have been vaccinated. The White House has shelved tougher options such as requiring post-arrival testing or requiring quarantines upon arrival in the U.S.

The White House has not yet acted to require domestic U.S. travelers to be vaccinated or get tested. Officials believe such a requirement would be mired in litigation.

"We base our decisions on the advice of the health and medical experts, what's going to be most effective and what we can implement," press secretary Jen Psaki said Thursday.

Biden is extending his directive requiring masks on airplanes and other public transit, which had been set to expire in January, through at least the middle of March, the White House said.

The administration is informing states that it has more than 60 teams available to help them or their municipalities address surges in cases and public health shortages heading into the winter.