With initial evidence of a diminishing surge in COVID-19, San Francisco leaders urged residents on Tuesday to stay home for New Year’s Eve and keep up the fight to contain the virus.

The reproductive rate in the city has been slashed by almost a quarter since the first week of December, Dr. Grant Colfax, the city’s public health director, said Tuesday in a virtual news conference. Average daily infections have fallen by the same amount just in the past week, according to this news organization’s analysis, and, on a per-capita basis, San Francisco is averaging fewer new cases than all but one other county in the Bay Area.

Ahead of the holiday, Colfax praised San Franciscans but urged them to practice caution. There is always New Year’s 2022, he said.

“Hundreds of families in San Francisco will have a chance to spend next New Year’s Eve together in good health because of the choices we make this week,” Colfax said. “As we head into New Year’s Eve, let’s remember the power is in our hands to continue to turn this surge around.”

In San Francisco, early action has made an impact, according to Colfax. On Dec. 5, the day before the city voluntarily implemented a stay-at-home order, the average sick person in San Francisco was infecting 1.45 others with the virus. By Dec. 26, three weeks later, the reproductive rate had been slashed to 1.13. In order to contain and suppress the virus, Colfax hopes to ring in the new year with a reproductive rate below 1.

Under the worst-case scenario in city models, where the reproductive rate stayed at 1.45, hospitals in the city would have been overrun with nearly 1,500 COVID-19 patients at a projected February peak, and more than 500 additional lives could have been lost by the beginning of March. At its current rate, hospitalizations are also projected to peak in mid-February but at close to 300 patients. If the reproductive rate in San Francisco falls below 1 by Jan. 1, it would result in hospitalizations peaking shortly thereafter and hundreds of lives saved, Colfax said.

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However, the city is walking a tightrope. An additional wave of infections from holiday celebrations would be “catastrophic,” Colfax said.

San Francisco’s counterparts across California have not fared as well. The state as a whole is leading the nation in per-capita infections over the past week, and hospitals are overrun in all of Southern California and the San Joaquin Valley.

To avoid that future, Colfax urged San Franciscans to keep up their resilience. Still, with the number of travelers over the holiday weekend at its highest since the onset of the pandemic, Colfax called what that could mean for the coming weeks “extremely concerning.”

The earliest the impact of Christmas celebrations may begin to show up in the data will be Jan. 2, Colfax said, and New Year’s Eve six days after that.

Despite the explosive spread elsewhere in the state, Colfax said there has been no evidence that the more virulent strain of COVID-19 from the United Kingdom had found its ways to California’s shores. Labs, including those at UC San Francisco, are sequencing test samples as they are taken, “so we would expect if and when this variant enters the country, the state or the region that it would eventually be detected,” Colfax said, though he stipulated “it is very likely it could be here and not yet detected.”