Before the winter surge, much of the bay area was celebrating low coronavirus transmission rates, which allowed for more relaxed restrictions on what people could do to have fun, work and live in general.
Now, case rates have plummeted again on the other side of that increase, and San Francisco reported its lowest case rate since the pandemic began – a year ago, when the city was in blockade mode. That was before a summer peak sent the numbers soaring, before a fall to lows in early October.
However, the picture across the bay area is uneven, with some counties still far from reaching the lowest levels seen last fall. And even as we approach lows, experts are concerned about the possibility of a fourth sudden increase in the coming weeks.
The lowest level reached by San Francisco, just before the winter peak, was a seven-day average of 2.8 infections per 100,000 inhabitants, recorded on October 1. Last week, the city hit a rate of 2.6 cases on Thursday, although the rate has since scored up to 3. San Francisco last recorded a lower case rate, 2.4, on March 20, 2020.
A concession stand with a mannequin and an encouraging sign was set up at the Teatro Sebastiani in Sonoma. Bay Area counties are looking forward to going back to the orange layer to reopen their savings, allowing more access to activities such as indoor dining and expanding to 50% of cinema capacity.
Yalonda M. James / The Chronicle
San Mateo County last week reported a rate of 3.95 cases, down from the rate of 4.35 reached in mid-October, before the start of winter. The county has also seen an increase since last week, to 6.5 on Sunday.
Sonoma County, which was struggling with high transmission even before the winter peak, finally saw its infections drop below 7, for the first time since June 30. On Sunday, the county reported a case rate of 6.5, well below the 8.2 pre-peak minimum on September 15.
Overall, the Bay Area’s infection rate is dropping close to its lower level of transmission seen in the fall. On Sunday, the seven-day average of new daily cases per 100,000 people was 5.9, slightly above the 5.2 low set on October 17.
Despite the good news, some counties are not yet close to their peak lows before winter. Napa County reported a rate of 6.8 on March 16, but jumped to 8.7 on Sunday, much higher than the rate of 3.5 on Labor Day.
Some counties, including Napa, do not report data on weekends or holidays, when the chances of reporting outliers are greater. Gaps in reports can create artificially low numbers for certain days and inflated numbers on days when reports are updated. State reporting agency lapses can also contribute to these single-day casualties if they create gaps for a few days with no new cases reported.
Marin County saw a rate of 2.5 per 100,000 cases on October 3, but only managed to drop to 3.9 on Thursday, before rising to 5.2 on Sunday. The counties of San Mateo, Contra Costa, Alameda and Solano observed similar patterns.
Across the state, rates fell dramatically, to 6.9 new cases per 100,000 residents on Sunday. This not only beats the October low of 7.5 before the winter wave, but marks the first time since before the summer wave that the number was below 7 – on 8 June.
This “honeymoon period” of decreasing case rates after a sudden increase left some experts concerned that a fourth increase could be on the way in late March or early April, fueled by variants of the coronavirus, namely variant B .1.1.7 that originated in the United Kingdom and is 50% more transmissible. Two California variants are also rapidly gaining ground in the state.
There are also lessons from when the state initiated a new color-coded level system in late August, linking the reopening to progress metrics against the virus. Most of the Bay Area started in the orange layer. Less than two months later, most were downgraded to purple after easing restrictions was accompanied by a setback in progress.
While it is unlikely to stimulate a peak as dramatic as that which occurred during the winter months, residents’ variations and complacency can push the curves back up before the majority of the population is vaccinated. The US Centers for Disease Control and Prevention has repeatedly raised this concern, as worrying variants spread and many states relax the restrictions of COVID-19.
“Increasingly, states are seeing an increasing proportion of their COVID-19 cases attributed to variants,” said CDC director Dr. Rochelle Walensky, during a meeting at the White House on Monday. “I am concerned that if we do not take the right measures now, we will have another preventable outbreak – just as we are seeing in Europe now and just as we are intensifying vaccination so aggressively.”
Mike Massa contributed to this story. Dan Kopf designed the graphics in this article.
Kellie Hwang is a writer for the San Francisco Chronicle. Email: [email protected]