Will XBB.1.5 spur another COVID surge?

If it feels like more people you know are getting COVID-19 lately, that may be true. Though the rise is relatively small, it marks a reversal of the downward trend the Bay Area had experienced since early December.

California’s public health leaders are keeping their fingers crossed that the state will be ready to move past the pandemic as the state of emergency comes to an end later this month, despite the recent uptick in coronavirus cases attributed to the fastmoving omicron subvariant XBB.1.5.

There are several reasons to be hopeful. This winter’s surge was milder than expected. Despite the added prevalence of the flu and respiratory syncytial virus, the state’s health care systems were not overwhelmed. And even as COVID-19 cases hit a peak in December, California did not see the serious outcomes it experienced during the first two years of the pandemic.

“The numbers were much, much lower than in prior surges as far as hospitalizations, ICU admissions and deaths,” Dr. Erica Pan, the state epidemiologist, told physicians during a webinar on Tuesday. “We have gotten to a point in this last winter where the hospital burden was much lower than prior surges.”

She said COVID-19 deaths were also lower than expected this season.

It is unclear whether those encouraging trends will hold as XBB.1.5, considered the most infectious strain of the coronavirus to date, extends its reach across the country.

The decline in coronavirus infections in California has stopped and numbers are edging back up, with the state’s health department reporting 2,893 average cases per day — or about 7.2 per 100,000 residents — as of Thursday, compared to 2,434 cases per day, or 6.1 per 100,000 residents, two weeks ago. That’s still well below the rate of 24.7 per 100,000 reported on Dec. 3, 2022.

With the number of official COVID tests performed in California dropping to record low levels due to the widespread use of home test kits whose results are not reported to authorities, Marin County’s public health department this week announced it will no longer report daily coronavirus case rates because those counts have become unreliable as a measure of community transmission.

Health officials say people should instead monitor wastewater data, from sources such as Stanford’s Wastewater SCAN dashboard. Recent samples from San Francisco, Alameda, Napa and Santa Clara counties show rises in viral levels in wastewater solids — in some cases, quite pronounced.

The upturn is especially noticeable in San Francisco and Oakland, where concentrations of SARSCoV-2 DNA in effluent have jumped since the end of January. The climb in Napa has been more gradual, while in San Jose, the most recent figures show a rise followed by a decline.

“People can click on sewer sheds that they live in or work in or live close to, and look at the trends in the wastewater and what the concentrations are now relative to what they were in the past,” said Alexandria Boehm, a wastewater surveillance expert at Stanford who has led surveys of sewage around the Bay Area. “That can help them understand what sorts of infections there are in the community. The change in concentration is related directly to changes in infections in the community.”

California last week topped 12 million total reported coronavirus cases since the start of the pandemic, according to data compiled by The Chronicle — a tally that’s likely an undercount and could increase substantially once XBB.1.5 grows in proportion.

The state’s seven-day rolling coronavirus test positivity rate, which tracks the percentage of lab test results that are positive for the virus, has nudged up to 6.4% from 4.9% two weeks ago. Epidemiologists consider a rate above 5% a threshold for community spread.

The positivity rate indicates directionality in test results, even if the number of tests administered is lower. But the current rate is still relatively modest; as recently as late December, the figure was much higher, at 12.7%.

The Centers for Disease Control and Prevention estimates that the XBB.1.5 omicron subvariant made up about 74.7% of cases nationally last week, with at least one new sublineage, XBB.1.5.1, that is also gaining ground. XBB.1.5’s prevalence in the Northeast region of the country is at 93.6%, while it is at 56.9% and growing in the Western Region.

“Whatever happens in the Northeast is a precursor for what will happen here,” said Boehm. “We’re starting to see signs that wastewater concentrations are starting to tick up at some of our plants. And that would not be surprising to me because we have a new variant. In the past, when we see a new variant make it into the population that is successful, we do see an increase in cases.”

But overall hospitalizations have fallen to levels they were at mid-November, indicating that even though XBB.1.5 will likely drive up infections it may not cause more severe disease. There are some signs that the new subvariant has lost some of its severity as it has spread.

“Outside the Northeast region during XBB.1.5’s rise, there was no surge in hospitalizations,” Dr. Eric Topol, director of the Scripps Research Translational Institute, tweeted last week.

The daily average of COVID patients in California hospitals now numbers 2,541, compared to 2,477 the previous week. Around 3% of the state’s inpatient beds are now in use for COVID-19 patients.

“In my clinic, we’re seeing a little bit more of a bump right now, not a fullon surge,” Dr. Christian Ramers, a specialist in infectious diseases and medical director of the Laura Rodriguez Research Institute in San Diego, told state physicians.

California is now approaching a milestone of 100,000 confirmed COVID-19 deaths since the start of the pandemic. As of Thursday, California had tallied 99,690 pandemic fatalities, with an average of 24 people still dying each day due to the virus.

State officials are optimistic that with wider uptake of the bivalent booster and treatments such as the antiviral Paxlovid, that number will not get much higher and California won’t see another devastating surge.

“Three years ago, this was the moment everybody was desperate for — that there was actually something to do when you tested positive,” Dr. Rita Nguyen, the state’s assistant health officer said.

The COVID-19 state of emergency in California will end on Feb. 28, but it is unlikely to affect most people. The order was put in place primarily to shift staff and resources to respond more quickly to the pandemic and to manage and distribute funds and supplies from the federal government. The end of any remaining restrictions will allow people to respond to the threat of the virus on an individual level.

It also marks the termination of any remaining mask mandates. Individual businesses and health providers may still require masks if they choose.

The end of the federal state of emergency on May 11, however, will shift COVID-19 vaccines, tests and treatments into the commercial market, with many people picking up at least some of the costs depending on their health insurance.