Graphics show how omicron is doing in San Francisco

In recent days, Bay Area media have reported a “skyrocket” in the number of COVID-19 cases in San Francisco and the Greater Bay Area, with some noting that the city and the region are posting records.

The increase in cases – which has led to a tightening of pandemic restrictions statewide – is not surprising given the ability of the omicron variant to cause infections in people vaccinated at a higher rate than the strains. earlier. In addition, it was generally expected that the holiday gatherings would lead to a winter wave.

Despite the increase in cases, the number of hospitalizations in the city has remained mostly stable – and it’s not just because of the lag between infection and hospitalization, experts say.


“It’s definitely a decoupling,” said Dr George Rutherford, epidemiologist at UCSF, of the relationship between case and hospitalization rates. “If it was like the waves of the past, we would have seen a greater [hospitalization] increase now. “

Even though vaccines are less effective at blocking infection and transmission than omicron, they are still very protective against serious illness and hospitalization (San Francisco has 80% of its total population vaccinated against the virus, and most other Bay Area counties have similar, if not higher, rates rates). There is also growing evidence that omicron causes milder symptoms than earlier variants such as delta and the original strain.

Rutherford said in the past, hospitalizations tended to increase 10 days after cases started to increase. The graph below shows that while this trend is true for the previous two waves – last winter’s wave and summer’s delta wave – it has yet to happen with omicron in San Francisco. The city believes that almost four out of five cases detected between December 17 and 20 were omicron.

“It’s just less serious,” Rutherford said of omicron. “Unless we’re ridiculously mistaken, things are different now.”

Cases began to increase in late November and, although hospitalizations have increased over the past month, they have not increased at the same rate as in the previous two waves. San Francisco also saw a small increase in cases during the first week of November – possibly triggered by Halloween gatherings – but the city has not seen a resulting increase in hospitalizations, further speaking decoupling of cases and hospitalizations. Delta was then the dominant variant in the region.

(The downward trend in the case curve on December 22 is likely due to weekend reporting delays, not a decrease in transmission of the virus.)

Rutherford isn’t the only UCSF expert who thinks the separation of case rates and hospitalization rates is real and not just a mirage of lag.

His colleague Dr Bob Wachter recently wrote in a viral Twitter thread that he doubts “the explanation” for which hospitalizations have not increased with the cases, is that it is “too early” to say it.

“If we reflected the severity of Delta, we would now see a big impact on hospital numbers,” Wachter wrote, later adding, “if the case-to-hospital ratios reflected Delta’s, I would expect at least 2 -3x those hospitalizations now. “

Rutherford and Wachter both expect an increase in hospitalizations in the coming weeks, but at a manageable level that is not comparable to past increases.

Rutherford also noted that the actual rate of inpatient cases will be even lower than reported, as many cases are caught by home testing not reported to city and state officials.

“We have given up on boxing this and hoping it goes away, it won’t happen,” he said. “It’s going to become endemic in humans, so the goal is to make it as less serious as possible. Vaccines and boosters are buying us that.”

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