After a week of rising Covid cases in Los Angeles, the county’s daily count of new infections hit a high not seen in nearly a year. On Christmas Eve the region reported 9,988 new cases. The last time it saw a daily new cases count that high was mid-January 2021.

On Tuesday of this week, L.A.’s new cases number stood at 3,052. That means the daily number of new infections has risen more than 300% in just four days. The 7-day average of test positivity — often considered a better gauge of virus spread because it is both a percentage and an average — is up over 400% in less than a week, from 2.3% on Saturday to 9.6% today.

The Omicron variant, while more transmissible, is thought to be less virulent than Delta, which it is rapidly replacing. That is good news, because it likely means fewer deaths in this fifth wave of the virus vs. other waves. The big unknown in that equation is whether, even with a reduced percentage of patients hospitalized, the rapid rise and overall number of infections will still overwhelm hospitals.

“If Omicron causes less severe illness, but infects many more people,” said county director of public health Barbara Ferrer this week, “let’s say 3% of people require hospitalization but we end up with 20,000 daily cases, that number could still cause severe stress on our healthcare system.”

While hospitalizations in Los Angeles County have remained fairly steady in the past week even as cases have skyrocketed, the last two days have seen an increase of 7%, from 749 patients with Covid to 801. That’s nothing like the 300% jump in new infections this week, but hospitalizations are a lagging indicator, often only spiking weeks after cases due to the incubation period of the virus.

Ferrer pointed to the “staggeringly fast rise” of cases in the U.K. and elsewhere “and the healthcare system strain that has followed” as a warning.

In New York, that state set another in a string of daily case records in the past week, recording 44,431 new infections in a 24-hour period. That’s more than double the record from last winter’s surge, which was just under 20,000 cases seen in one day.

The U.S., meanwhile, moved toward its own grim new daily cases record. On Thursday, Johns Hopkins University tallied 261,339 infections in 24 hours. That’s the third highest total ever for the nation, behind only counts of 288,610 and 295,879 recorded in January of this year. With a current test positivity of 15.1% and rising, the U.S. is likely to break that daily record very soon.