LOS ANGELES >> The new COVID-19 subvariants collectively nicknamed FLiRT are continuing to increase their dominance nationwide, fueling a rise in cases in Los Angeles County and growth in the coronavirus levels seen in California wastewater.

Taken together, the data point to a coronavirus resurgence in the Golden State — one that, while not wholly unexpected given the trends seen in previous pandemic-era summers, has arrived earlier and is being driven by even more transmissible strains than those previously seen.

It remains unclear how bad the COVID situation may get this summer, however. Doctors have said that by the Fourth of July, we may have a better feel for how the rest of the season will play out.

The U.S. Centers for Disease Control and Prevention estimates that the FLiRT subvariants — officially known as KP.3, KP.2 and KP.1.1 — make up a combined 62.9% of specimens nationwide for the two-week period ending Saturday. That’s up from 45.3% a month ago.

Experts say the new subvariants are more contagious than the winter’s dominant subvariant, JN.1.

California is now one of 15 states with high or very high coronavirus levels in sewage, according to the CDC. Those states are generally in the West and the South, as well as New England. Besides California, they are Alaska, Colorado, Connecticut, Florida, Hawaii, Idaho, Missouri, Nevada, New Hampshire, New Mexico, Tennessee, Texas, Utah and Wyoming.

Hawaii’s latest variant report shows the proportion of the FLiRT subvariants continued to grow in the islands over the past month.

Hawaii’s lab also has detected the LB.1 variant, a descendant of JN.1, via genome sequencing of COVID PCR-positive test specimens collected from across the state.

Coronavirus levels in California wastewater overall have sharply increased since early May, a contrast to national trends, which indicate a slower rise. California’s latest weekly wastewater viral activity level was near the peak seen last summer.

In Santa Clara County, Northern California’s most populous, the levels in wastewater are considered high across a wide swath of Silicon Valley, from San José to Palo Alto.

Coronavirus levels in L.A. County wastewater have remained generally stable after rising last month. For the week ending June 8, the most recent available, levels in sewage were at 15% of the peak from the winter of 2022–23 — up from 13% the prior week, but down slightly from 16% the week before that. Last summer peaked near the end of the season, when levels in sewage were at 38% of the 2022–23 winter height.

Reported COVID-19 cases continue to rise, though. For the seven-day period that ended June 16, there were an average of 154 per day reported in L.A. County, up from 121 the prior week. Reported cases are an undercount, as they indicate only tests done at medical facilities, and don’t include at-home tests. Nor do they reflect that far fewer people are testing for COVID when they’re sick.

The daily average number of people with COVID in L.A. County hospitals is also ticking up. There were an average of 138 per day for the week that ended June 15, up from 126 the week before.

COVID deaths remain stable, at fewer than one per a day, on average, for the week that ended May 28.

The percentage of COVID tests at California’s medical facilities that are coming back with positive results continues to climb. For the week that ended June 17, 7.5% of statewide COVID tests came back positive, well above the 3.1% rate from a month ago. Last summer’s peak was 13.1%, recorded at the end of August.

The California Department of Public Health in June updated its guidance for older adults, “especially those with weakened immune systems.” Officials urged older people to stay up to date on vaccines, seek medication if sickened with COVID, and to consider extra precautions, such as wearing a mask in crowded indoor areas, opening windows and doors to increase ventilation, staying away from sick people, washing their hands often, and covering up coughs and sneezes.

The increases in certain coronavirus tracking data come as the U.S. Food and Drug Administration in mid-June released new advice for vaccine manufacturers. In a June 13 statement, the agency urged that manufacturers, if feasible, design this autumn’s vaccine formula against KP.2 — one of the FLiRT subvariants — instead of its parent, JN.1.

The new recommendation overrides guidance from just a week earlier, when the agency had advised the vaccines to be designed against JN.1.

“This change is intended to ensure that the COVID-19 vaccines (2024-2025 formula) more closely match circulating SARS-CoV-2 strains,” the FDA said in a statement, referring to the formal name of the COVID-19 virus.

By this autumn, the prevailing COVID subvariant “will probably be closer to KP.2 than they would have been, perhaps, to JN.1,” said Dr. Peter Marks, director for the FDA’s Center for Biologics Evaluation and Research, in a press briefing Friday.

The mRNA-based vaccines, made by Pfizer and Moderna, will be able to produce shots this fall for KP.2. But the protein-based vaccine, made by Novavax, will remain designed against JN.1 — as mRNA vaccine manufacturing can be done more quickly, Marks said.

“What you can do when you’re making a protein-based vaccine versus an mRNA vaccine is different in terms of the agility to react to what’s coming up,” Marks said. Still, the difference between getting a vaccine designed against the newer KP.2 subvariant versus the slightly older JN.1 subvariant will probably not result in “that big of a difference.”

“We’re not going to have a preference,” Marks said, in terms of making a recommendation of the Pfizer or Moderna vaccine over Novavax. “The best vaccine for going into this fall season is the one that you put in your arm.”

Marks said a vaccine designed against KP.2 “perhaps brings a little benefit” over one against JN.1. “By essentially using the freshest update, we hope to provide protection immunity that will last longer,” Marks said, into the late autumn and the winter.

“It’s like trying to give people the greatest edge, right? The one-hundredth of a second extra that you win [a race] with,” Marks said. “But I think the most important thing for people to know is, either way, either of these is perfectly good to get.”

Federal officials expressed hope that the COVID vaccine would be made available earlier this year than in 2023. Last year’s rollout was complicated because the updated COVID vaccine came out slightly later than the seasonal flu shots, making it more difficult for people to get both vaccinations at the same visit if they would’ve preferred that.

COVID-19 continues to remain a disease to guard against, doctors say. About 45,000 COVID deaths have been reported since Oct. 1 nationally, and doctors say those most at risk are older and immunocompromised people who haven’t received an up-to-date vaccination.

“This isn’t just going away into the night. It’s hanging around,” Marks said.

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