WASHINGTON — US President Joe Biden announced Thursday a winter campaign against Covid-19, with new testing requirements for travelers and a surge in vaccination efforts as the new Omicron variant threatens to revive the pandemic.

Biden has brought steady leadership after the chaotic Donald Trump years, but the mutating coronavirus continues to defy him, helping drive his approval ratings deep underwater.

Urging the nation — in particular his political rivals — to unite behind the strategy, Biden unveiled a raft of actions designed to tamp down Covid-19 in the coming months, as the latest Omicron variant spreads worldwide.

“It’s a plan that I think should unite us,” Biden said, speaking from the headquarters of the National Institutes of Health in a Washington suburb.

“I know Covid-19 has been very divisive. In this country, it’s become a political issue,” he added. “A sad, sad commentary. It shouldn’t be, but it has been.”

Ten cases of the new strain have so far been confirmed in the United States, including five in New York announced Thursday evening by state Governor Kathy Hochul, one in Los Angeles county and one in the Pacific island state of Hawaii.

The Hawaii case and one in Minnesota both involved residents with no recent international travel history, signaling the strain is already circulating inside the country.

“This is a case of community spread. The individual has no history of travel,” the Hawaii Health Department said.

Biden’s updated actions include the requirement that all inbound international travelers be tested within one day of flying.

This will apply to all travelers, both American and foreign, regardless of vaccination status, a US official said.

For domestic travelers, Biden will announce he is extending a mask mandate on airplanes, trains and other public transport through mid-March.

White House spokeswoman Jen Psaki told reporters testing and vaccine requirements could eventually be added to domestic flights too. “Nothing is off the table,” she said.

The barrage of measures is partly meant to reassure Americans that Biden is doing everything possible to prevent the pandemic from derailing the impressive US economic recovery — and the winter holidays.

In addition to his public rollout, Biden penned a column for the Friday edition of the large-circulation USA Today national newspaper to assuage Americans’ “unease” about the new variant and Covid in general.

“We will beat it back with science and speed, not chaos and confusion -– just as we did in the spring and again with the more powerful delta variant in the summer and fall,” the president wrote.

Biden and his aides have recently stressed there will be no return to mass shutdowns.

But the White House also faces the challenge that many Americans are not receptive to Biden’s appeals for collective action.

Despite ever-more creative attempts to encourage people to get their shots, about 40 percent of the country have yet to be fully vaccinated, and booster rates are lagging too.

Nationwide campaign

Biden said a surge in outreach on vaccines and booster shots was being launched, with a nationwide campaign targeting recipients of Medicare public health care. The government will team up with AARP, a large lobbying group representing people aged 50 and over.

At the other end of the age scale, the Biden administration will try to ensure that schools do not return to mass lockdowns.

“We’re expanding our efforts to vaccinate children, ages five and up,” said Biden. “For any parent worried about the Omicron variant or the Delta variant, get your child vaccinated at one of the 35,000 locations in the country.”

In another bolstering of existing policies, the White House will encourage the use of home testing kits by announcing that health insurance must cover 100 percent of the cost.

For those without health insurance, there will be an increase in the availability of free kits.

The kits currently sell for around $25, as opposed to being available either for free or at nominal costs among peer nations in Europe.

Meanwhile, the White House stressed that the administration’s restrictions on travelers from eight southern African countries over growing Omicron fears was not a “punishment” to those nations but a safety measure.

“We of course are in close touch at a diplomatic level with leaders in these countries about the steps we’re taking,” Psaki said, referring to the ban imposed last week on US arrivals from South Africa, Botswana and other nations.

“It’s not meant to be a punishment,” she added. “It is steps recommended by our public health officials and medical experts in order to delay the spread of a variant.”