Five months after President Joe Biden declared the U.S. to be on the verge of defeating COVID-19, the virus threatens a winter resurgence across the country.

Biden will sketch out on Thursday his latest plan to quell the pandemic that’s dogged his presidency, with two U.S. cases of the omicron variant now confirmed and threatening to fuel an already high case count. His latest measures include requiring private insurers to reimburse the cost of at-home tests, stricter testing requirements for air travelers arriving from abroad and extending a mask mandate.

Cases are already building in cold-weather states where Americans have begun to retreat indoors, where schools have been linked to outbreaks and where public health officials say they face widespread exhaustion with measures intended to prevent infections. Biden’s response is further complicated by omicron, which features mutations scientists believe could make it more transmissible and virulent.