This is now California’s worst summer COVID wave in years. Here's why

A group of people on a sidewalk in Laguna Beach.

Aug. 12, 2024 Updated 10:33 AM PT

California’s strongest summer COVID wave in years is still surging, and an unusual midsummer mutation may be partly to blame.

There are a number of possible culprits behind the worst summer infection spike since 2022, experts say. A series of punishing heat waves and smoke from devastating wildfires have kept many Californians indoors, where the disease can more easily spread. Most adults are also well removed from their last brush with the coronavirus, or their last vaccine dose — meaning they’re more vulnerable to infection.

But changes in the virus have also widened the scope of the surge.

Of particular concern is the rise of a hyperinfectious subvariant known as KP.3.1.1, which is so contagious that even people who have eluded infection throughout the pandemic are getting sick.

“COVID is extraordinarily common now,” said Dr. Elizabeth Hudson, regional chief of infectious diseases for Kaiser Permanente Southern California’s 16-hospital healthcare system.

COVID hospitalizations are ticking up, but remain lower than the peaks for the last two summers, probably thanks to some residual immunity and the widespread availability of anti-COVID drugs such as Paxlovid.

The World Health Organization has warned of COVID infections rising around the world, and expressed concern that more severe variants could emerge.

“In recent months, regardless of the season, many countries have experienced surges of COVID-19, including at the Olympics,” said Dr. Maria Van Kerkhove, the WHO’s technical lead on COVID.

Among those caught up was 27-year-old American sprinter Noah Lyles, who after winning the gold in the men’s 100-meter finals, came up short Thursday during the 200-meter finals, taking the bronze. Lyles collapsed after the race, fighting shortness of breath and chest pain, and was later taken away in a wheelchair.

“It definitely affected my performance,” he said of the illness, estimating that he felt “like 90% to 95%” of full strength.

The rate at which reported coronavirus tests are coming back positive has been rising for weeks — to above 10% globally and more than 20% in Europe. In California, the coronavirus positive test rate was 14.3% for the week that ended Aug. 5 — blowing past the peaks from last summer and winter — and up from 10% a month ago.

There were already indications in May that the typical U.S. midyear wave was off to an early start as a pair of new coronavirus subvariants — KP.2 and KP.1.1, collectively nicknamed FLiRT — started to make a splash, displacing the winter’s dominant strain, JN.1.

But by July, a descendant strain, KP.3.1.1, had clearly taken off.

“KP.3.1.1 is extremely transmissible and a little bit more immune evasive. It kind of came out of the blue during the summer,” said Dr. Peter Chin-Hong, an infectious-diseases specialist at UC San Francisco.

Cases are up at Kaiser Permanente Southern California, and “looking through the CDC data ... KP.3.1.1 is really what is driving this particular surge,” Hudson said. “We are certainly much higher than we were last summer.”

Anecdotally, some infected people report being “pretty darn miserable, actually — really severe fatigue in the first two days,” Hudson said.

People may want to think their symptoms are just allergies, she said, but “it’s probably COVID. So we’re just really encouraging folks to continue to test.”

An initial negative test doesn’t necessarily mean you’re out of the woods, though. Officials recommend testing repeatedly over as many as five days after the onset of symptoms to be sure.

California has now reported four straight weeks with “very high” coronavirus levels in its wastewater, according to data released by the U.S. Centers for Disease Control and Prevention on Friday. That followed five weeks of “high” viral levels.

Line chart shows COVID levels in wastewater. For the week ending on Aug. 3, the California level is 13.2, considered very high. Nationwide, the level is very high at 9.01.

Last summer, California recorded only eight weeks with “high” coronavirus levels in wastewater, and never hit “very high” levels. In the summer of 2022, California spent 16 weeks with “high” or “very high” levels of coronavirus in wastewater.

“Fewer people got immunized this year compared to last year at this time,” Chin-Hong said. “That means, particularly amongst people who are older, they’re just not equipped to deal with this virus.”

There are 44 states with “high” or “very high” coronavirus levels in their wastewater, according to the CDC. Five states, and the District of Columbia, have “moderate” levels, and there were no data for North Dakota.

The CDC said coronavirus infections are “growing” or “likely growing” in 32 states, including California; are “stable or uncertain” in seven states, as well as the District of Columbia; are “likely declining” in Connecticut; and “declining” in Hawaii and Nevada. There were no estimates in eight states.

In Los Angeles County, coronavirus levels in wastewater jumped to 54% of last winter’s peak over the 10-day period ending July 27, the most recent available. A week earlier, coronavirus levels in wastewater were at 44% of last winter’s peak.

For the week ending Aug. 4, L.A. County reported an average of 479 coronavirus cases a day, double the number from five weeks earlier. Cases are an undercount, only reflecting tests done at medical facilities — not self-tests conducted at home.

In Santa Clara County, the most populous in the San Francisco Bay Area, coronavirus levels were high in all sewersheds, including San Jose and Palo Alto.

Hospitalizations and emergency room visits related to the coronavirus are also rising. Over the week ending Aug. 3, there were an average of 403 coronavirus-positive people in hospitals in L.A. County per day. That’s double the number from five weeks earlier, but still about 70% of last summer’s peak and one-third the height seen in summer 2022.

For the week ending Aug. 4, 4% of emergency room encounters in L.A. County were classified as related to the coronavirus — more than double the figure from seven weeks earlier. The peak from last summer was 5.1%.

“We’ve had a few people who have become very ill from COVID. Those are people who tend to be pretty severely immunocompromised,” Hudson said.

UC San Francisco has also seen a rise in the number of coronavirus-infected hospitalized patients. As of Friday, there were 28, up from fewer than 20 a week earlier, Chin-Hong said.

In the Bay Area, three counties have urged more people to consider masking in indoor public settings because of the COVID surge. Contra Costa County’s public health department “recommends masking in crowded indoor settings, particularly for those at high risk of serious illness if infected,” the agency said Tuesday, following similar pleas from San Francisco and Marin County health officials.

Compared with advice such as washing hands and staying away from sick people, suggesting wearing a mask can provoke strong opposition from some.

“The moment people see this, like in their mind, it sets off this chain reaction of, like, all the negative things of the pandemic, having to have society shut down and social isolation,” said Dr. Abraar Karan, an infectious-disease doctor and researcher at Stanford University.

But masks do help reduce the risk of infection, and people don’t have to wear them all the time to benefit. Karan says he socializes and eats at indoor restaurants. But he’ll decide to mask in other situations, like “when I’m traveling,” and, obviously, at work.

Doctors say that wearing a mask is one of many tools people can use to reduce their risk, and can be especially helpful when in crowded indoor settings.

Karan said he’s seen more coronavirus-positive patients while working shifts in urgent care, and he suggested that more healthcare providers take the time to order tests. He said he worries that when people come in with relatively mild symptoms, they may be sent home without testing.

But that could miss potential COVID diagnosis, which could allow a patient to get a prescription for an antiviral drug like Paxlovid.

Without testing, “you run the risk of taking shortcuts and not prescribing people meds that they actually should technically be getting,” Karan said.

Times staff writer David Wharton contributed to this report from Saint-Denis, France.