The Bay Areas summer COVID-19 surge is winding down as case numbers reach levels last seen in April.

With no new coronavirus variants of concern on the horizon, the region appears headed for a welcome respite in the pandemic. And as early as next week, the federal government could start shipping out updated booster shots that target the latest omicron sublineages and could help extend vaccine protection well into the fall.

Despite the many reasons to feel optimistic, Bay Area health experts caution that weve been here before and that the coronavirus remains an unpredictable foe.

Its tough to say where were going to head next, said Abraar Karan, an infectious disease doctor at Stanford. We dont know when the next big surge is going to be, but we do know in the winter months we have seen resurgences.

One challenge going forward is that tracking case numbers has become increasingly difficult with so many people now testing at home results of which are not usually recorded with the state or counties or not testing at all. The problem could be exacerbated starting Friday, when federal officials are set to stop sending out free, at-home COVID test kits through the mail due to a lack of funding.

As of Tuesday, the Bay Area reported a seven-day average of 18 daily coronavirus infections per 100,000 residents, according to state figures, while Californias seven-day average fell to 21 per 100,000, down from 37 three weeks ago. The statewide test positivity rate has plunged to 8.7% but remains well above the 1.2% average recorded in mid-March following the winter surge.

Schools across the state are reopening without virus mitigation measures that were in place last year but some students are still wearing masks.

COVID deaths, however, have plateaued with the state now averaging 45 per day. The Bay Area is reporting 14 deaths a day, up from just 5 a day recorded a month ago. Hospitalizations also remain stubbornly elevated, with 3,108 patients tallied in California on Tuesday, including 540 in the Bay Area roughly the same numbers recorded in mid-June.

Ive been so humbled by the virus, Im reluctant to make any predictions, said John Swartzberg, an infectious disease expert at UC Berkeley. The good news is were coming out of the surge. But that doesnt give me a great deal of comfort because when we reached our nadir the week before Thanksgiving last year, Southern Africa experienced omicron and within six weeks we were in the worst part of the pandemic we ever experienced.

We didnt see it coming until it hit us right in the face, he said, referring to the largest though not deadliest wave of the pandemic yet.

The highly contagious and immune-evasive omicron subvariant BA.5 is still the dominant strain of the virus, making up about 94% of the sequenced coronavirus cases in the Northern California region, trailed by the newer BA.4.6. There are currently no other variants raising red flags, the experts said.

I would say the caseload is still decently high, said Karan. All the metrics are trending downward, but where that settles is unclear.

Other factors could slow the downward trends or even cause a new upswing in the fall, however.

Schools across the state are reopening without virus mitigation measures that were in place last year, in alignment with updated guidance from the U.S. Centers for Disease Control and Prevention that no longer calls for masking inside classrooms or surveillance testing for students and staff.

The number of people getting reinfected with the virus also could create a long tail of infections before the surge fully subsides, especially as shorter days and cooler months arrive and people spend more time indoors.

The things we know contribute to these surges are still in play, Swartzberg said, adding that human behavior could play a role in what comes next. Whats different this year is people have decided the pandemic is over or of negligible import and are acting accordingly.

Dr. Bob Wachter, UCSF chair of medicine, said in a lengthy Twitter thread over the weekend that he still plans to abstain from indoor dining and don a mask in crowded rooms until daily case rates fall below 5 for every 100,000 people in the region. But that puts him in the minority, with a growing number of Americans saying they have returned to living their normal pre-pandemic lives, according to a national survey.

Were facing other forces, Karan said. Were facing politicians who want to move on. Were facing fatigue, where people dont care about getting infected anymore. I see a lot of people trying to downplay the virus because they dont want to change behaviors or see policies they consider intrusive, such as mask mandates.

That could be a dangerous attitude, experts say.

If the general public assumes the pandemic is over, already sluggish vaccine uptake could mean fewer people line up for the new bivalent COVID boosters that target both earlier strains of the virus and later variants in the omicron family.

Only two-thirds of the U.S. population is fully vaccinated, and less than half of those have received their first booster dose, according to the latest figures from the CDC.

And despite the widespread availability of new drugs and treatments that cut down the number of virus-related hospitalizations and deaths, there is increasing concern now about the potential impact of long COVID, which the government has just started researching. Between 2 million and 4 million people are out of work due to the symptoms of the persistent condition, according to a recent report from the nonpartisan Brookings Institution.

It's a mixed bag right now, Swartzberg said. The big question mark is what this virus is going to decide to do. The other question is, what are people going to decide to do?

Aidin Vaziri is a San Francisco Chronicle staff writer. Email: avaziri@sfchronicle.com

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Bay Area's summer COVID surge is nearly over. What happens next? - San Francisco Chronicle