SAN FRANCISCO (AP) — California reported 669 COVID-19 deaths, the second-highest daily death count, on Saturday and the nation’s most populous county announced it had detected its first case of a more transmissible strain of the coronavirus.

Public health authorities in Los Angeles County confirmed its first case of the variant of COVID-19 first detected in the United Kingdom. It was identified in a man who recently spent time in the county. The man has traveled to Oregon, where he is isolating.

Although this is the first confirmed case of the variant, health officials believe it is already spreading in a county that surpassed 1 million coronavirus cases on Saturday. Although the variant does not appear to make people sicker, it spreads more easily, which could result in more infections, and with them, additional hospitalizations in a region hit hard by the surge.

“The presence of the U.K. variant in Los Angeles County is troubling, as our healthcare system is already severely strained with more than 7,500 people currently hospitalized,” said Barbara Ferrer, director of the county’s Department of Public Health.

The state has been seeing more than 500 deaths and 40,000 new cases daily for the past two weeks, and many regions, especially in the south, have seen their hospitals and especially intensive care units overwhelmed.

Lawmakers and public health officials have said mass vaccinations are the key to flattening the surge, but they’re increasingly concerned about the rocky rollout of the vaccine.

A center that can handle as many as 12,000 shots a day opened Friday at Dodger Stadium in Los Angeles but Gov. Gavin Newsom and others said they had no idea when, if or how many doses will arrive from the federal government.

Newsom said that he and other governors were told earlier this week that a reserve supply of 50 million doses would be distributed. California has received more than 3.5 million doses of the vaccine and has administered over 1 million doses, while anticipating hundreds of thousands more.

Michael Pratt, a spokesman for the U.S. Department of Health and Human Services, said there has been no reduction in doses shipped to states.

But around the state, counties said they were struggling to make vaccination plans and said mass inoculations of people 65 and older, who represent most COVID-19 deaths, will have to wait, despite Newsom this week adding them to the eligibility list.

Instead, they are focusing on those at the head of the eligibility line: health care workers and the most vulnerable seniors in nursing homes. In addition, it takes two separate doses spaced weeks apart to ensure the most complete virus protection, health experts say.

Without a steady and predictable supply, long-range planning for vaccine distribution is challenging, said Dr. Paul Simon, chief science officer of the Los Angeles County Department of Public Health.

The county— the nation’s most populous with 10 million residents — is struggling to vaccinate its 800,000 health workers and doesn’t anticipate being able to provide large-scale inoculations of its 1.3 million people 65 and older until February, Simon said.

“We don’t need the full supply to begin vaccinating,” Simon said. “But there will be a heck of a lot of frustration if we open it up for that many people and there’s a very little supply of vaccine to serve them.”

The city of San Francisco announced it’s ready to handle 10,000 people a day at mass vaccination sites but can’t put the plans in motion because it’s unclear how many doses will be available.

Meanwhile, demand is soaring despite the confusion.

Kaiser Permanente said requests for vaccination appointments had overloaded its phone and online appointment systems. The health care giant said it received more than 90,000 calls to its vaccine hotline on Thursday.

“But the problem is we do not have enough vaccine supply on hand to meet even a fraction of this demand,” it said.

Other cases of variant B.1.1.7 have been reported in Ohio, New York, Pennsylvania, Georgia, Connecticut, and Florida among others.