The White House, in an evolving scramble to slow the spread of COVID-19, urged people Monday not to gather in groups of larger than 10 people for the next 15 days.

The guidance comes less than 24 hours after the Centers for Disease Control and Prevention recommended that gatherings of more than 50 people be canceled over the next eight weeks. The stronger recommendations come as more state and local officials are seeking to keep people at home in the coming weeks by ordering restaurants, bars and gyms to close.

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The White House guidelines also recommend that people avoid going to restaurants or bars and that people work or engage in schoolwork from home whenever possible as officials seek to control the pandemic.

Deborah Birx, the White House coronavirus response coordinator, said officials have been closely following models, including in coordination with groups in the United Kingdom, that showed that social distancing and staying in small groups is most effective for containing the new coronavirus that causes COVID-19.

“The most important thing was if one person in the household became infected, the whole household self-quarantine for 14 days,” she said.

The administration is urging people not to visit nursing homes or long-term care facilities, where residents appear at higher risk for contracting the virus, in the next 15 days.

Officials also encouraged people to avoid discretionary travel, shopping trips and social visits.

During a press briefing, President Donald Trump said the administration is not yet instituting stronger guidance, such as ordering people to stay home or imposing a national curfew.

The administration hopes to avoid domestic travel restrictions, although they are “something that we talk about every day,” he added.

When asked if he will order that restaurants and bars close for in-person service, Trump said, “That could happen, but we haven’t gotten there yet.”

No vaccine exists for COVID-19, but the National Institutes of Health announced Monday the beginning of a Phase 1 clinical trial for one. The vaccine, which is being developed by NIH and biotech company Moderna Inc., will involve injections 28 days apart. The trial began at Kaiser Permanente Washington Health Research Institute in Seattle and includes 45 people who will be followed for the next year.

In the meantime, as fears about the health care system’s ability to handle a crush of COVID-19 cases rise, Trump told the nation’s governors on a call earlier in the day that they should go ahead and order ventilators or respirators if hospitals in their states need more and they have access to a supply chain.

“It’s always going to be faster if they can get them directly if they need them, and I’ve given them direction to order directly” rather than rely on the federal government, he told reporters.

Trump said the federal government has stockpiles and is ordering “tremendous numbers” of ventilators, respirators and masks.

Washington Democratic Gov. Jay Inslee asked the White House to prioritize providing ventilators and respirators to states with the most COVID-19 cases after Trump said states shouldn’t rely on the federal government for such equipment, Inslee spokesman Mike Faulk said. 

“We, obviously think that the federal government should continue to be a partner on this,” he added.

Jacob Fischler contributed to this story.