A pair of newly reported deaths in California have challenged the longstanding timeline of the coronavirus pandemic, raising new questions about when and how the virus first arrived in the U.S. and the costs of the nation’s lack of preparation earlier in the winter.

The first U.S. death from the coronavirus took place in early February, according to a county in the San Francisco Bay Area, nearly three weeks earlier than U.S. health authorities had previously realized.

Officials in Santa Clara County said they learned Tuesday that a 57-year-old woman who died on Feb. 6 and a 69-year-old man who died on Feb. 17 had Covid-19, the respiratory disease caused by the coronavirus. Officials couldn’t determine exactly how they picked up the virus, as neither had been to China or another overseas virus hot spot.

Previously, the first known U.S. deaths from Covid-19 involved two people in the Seattle area who died Feb. 26. Both had been residents at a Kirkland, Wash., nursing home that was the scene of the first serious U.S. outbreak.

“None of these cases had a significant travel history,” Sara Cody, Santa Clara County’s health officer, said at a press conference. “We presume that each of them represent community transmission.”