As restrictions ease in more Bay Area counties, experts remember the calm before the last surge.

In a welcome turnaround, four Bay Area counties are now in Calfornia’s orange reopening tier. Yet elation over the latest easing of coronavirus restrictions was tempered by memories of what happened the last time officials loosened the rules.

Coronavirus trends were similarly positive in the fall, when the region’s move to the orange tier was quickly followed by a rapid rise in cases.

This time around, we’re in a different place. A growing number of people are getting vaccinated. But many experts remain cautiously optimistic as San Francisco, Marin and Santa Clara counties now join San Mateo County in the orange tier of California’s reopening plan, the secondleastrestrictive level. “There’s a very good chance we’re going to have a brief honeymoon and then we’re going to be surprised,” said infectious disease specialist Stefano Bertozzi of UC Berkeley. “There is a future where this goes on much longer than we hope.”

In late October, six of the Bay Area’s nine counties were in the orange tier, and San Francisco even made it to the least restrictive yellow tier. The Bay Area average infection rate was just under 7 cases per 100,000 people. Just two weeks later, the number shot up to 11. By midNovember, the state’s “emergency brake” on reopening plunged most Bay Area counties to the most restrictive purple tier.

Today, case rates around the Bay Area are looking similar to what they were back in October, and last week San Francisco hit its lowest coronavirus case rate since one year ago. Two more counties could join the orange tier next week.

Though case rates, hospitalizations and deaths are dropping, experts are eyeing the history with concern. Even with more people getting vaccinated every day, they worry increased complacency could lead to a fourth surge.

Though it’s early to say if Bay Area backsliding may occur in the coming weeks, data now is showing a slight uptick in several counties from when redtier metric requirements were relaxed on March 12. The small increases, which could possibly be partially attributed to lags in reporting times, are in Marin, Napa, San Mateo and Solano counties. Overall, California and the Bay Area continue to trend downward, a positive direction.

Experts also are watching an uptick in daily new cases in more than half of U.S. states amid a rapid lifting of restrictions and spring break partying. Some European nations are implementing strict lockdowns as new variants threaten their progress.

Sara Cody, Santa Clara County’s health officer, told the Board of Supervisors on Tuesday that the move to orange is encouraging but at the same time, “We are just not out of the woods.”

“We are beginning to see signs that we are stalling out,” she said.

Marin County Public Health Officer Matt Willis also stressed a need to “stay the course.”

“The next four weeks are pivotal for us,” he said. “We saw an uptick in cases last week and with variant cases increasing, we don’t want to drop the ball before we reach the goal line. Letting your guard down puts us at risk of slipping backward.”

Monica Gandhi, a UCSF infectious disease expert, took an upbeat view, predicting that vaccination and other factors this time around will lead to a very different outcome.

“This is totally different; something massive has changed in the world,” she said. “I’m 100% certain there will not be a fourth surge.”

She noted the high vaccination rates and comparatively slow lifting of restrictions in Israel and the U.K., and that those countries have yet to see another surge despite the emergence of coronavirus variants. In Israel, 60% of people have received at least one vaccine shot and in the U.K. it’s 50%.

In the U.S., 25% have received at least one shot, which Gandhi characterized as actually quite high. She said the increasing pace of Bay Area vaccinations, in San Francisco especially, along with slower easing of restrictions compared to much of the U.S., will help prevent another virus spike.

Her view was not shared by infectious disease experts at a forum hosted by UCSF on Tuesday, where Bertozzi of UC Berkeley referred to this as a “brief honeymoon” period.

Peter ChinHong of UCSF likened today’s position to that of the summer surge, rather than the winter one, due to increased numbers of people traveling. The Midwest was surging then and the spread moved west to Arizona and Nevada.

“It feels like this is like that again,” he said in an interview. “It’s like the summer surge when we didn’t see all those ICU beds being used and hospitalizations were relatively controllable. We’ll probably see that, but maybe with fewer hospitalizations.”

Spring break traveling partiers are also at it again, ChinHong noted, voicing worry that overall complacent behavior has increased and testing behavior has dropped off. He said there’s likely more transmission than is known.

“COVID bombs go off simultaneously,” he said. “When you increase, you increase a lot, very fast. That’s what we’ve learned every single time.”

George Rutherford, also a UCSF infectious disease expert, was hopeful but wary for the next several weeks.

“We’re in a much better place this time around, but we’re not in a perfect place,” he said.

In addition to spring break, upcoming holidays, including Easter and Eid alFitr, could be potential “amplifying events,” he said. Importantly, most Bay Area counties still haven’t reached their prewinter surge lowest case rates, which Rutherford said means there is still transmission happening.

“That concern remains,” he said. “The prescription is the same: wear a mask, stay socially distanced, and when your turn comes, get vaccinated.”