COVID-19 appears to be on the rise in some parts of California as a new, highly contagious subvariant — featuring “razor blade throat” symptoms overseas — is becoming increasingly dominant.

Nicknamed “Nimbus,” the new subvariant NB.1.8.1 has been described in news reports in China as having more obvious signs of “razor blade throat” — what patients describe as feeling like their throats are studded with razor blades.

Although “razor blade throat” may seem like a new term, the description of incredibly painful sore throats associated with COVID-19 has emerged before in the United States, like having a throat that feels like it’s covered with shards of glass. But the increased attention to this symptom comes as the Nimbus subvariant has caused surges of COVID-19 in other countries.

“Before Omicron, I think most people presented with the usual loss of taste and smell as the predominant symptom and shortness of breath,” said Dr. Peter Chin-Hong, a UC San Francisco infectious-disease expert. But as COVID has become less likely to require hospitalization, “people are focusing on these other aspects of symptoms,” such as an extraordinarily painful sore throat.

Part of the Omicron family, Nimbus is now one of the most dominant coronavirus subvariants nationally. For the two-week period that ended June 7, Nimbus comprised an estimated 37% of the nation’s coronavirus samples, now roughly even with the subvariant LP.8.1, probably responsible for 38% of circulating virus. LP.8.1 has been dominant over the past few months, according to the Centers for Disease Control and Prevention.

The Nimbus subvariant has also been increasing since May in California, the state Department of Public Health said in an email to the Los Angeles Times. Projections suggest the Nimbus subvariant comprises 55% of circulating virus in California, up from observations of just 2% in April, the agency said Friday.

“We are seeing some indicators of increased COVID-19 activity, including the rise of the NB.1.8.1 variant, elevated coronavirus levels in wastewater, and an uptick in the test positivity rate,” Dr. Elizabeth Hudson, regional chief of infectious diseases for Kaiser Permanente Southern California, wrote in an email to The Times.

“Wastewater surveillance across Southern California shows variability: Santa Barbara watersheds are reporting moderate-to-high levels, Ventura and Los Angeles counties are seeing low-to-moderate levels, Riverside is reporting low levels, while San Bernardino is experiencing high activity,” Hudson said.

While viral concentrations remain relatively low, Los Angeles County has observed an increase in coronavirus levels in sewage, the local Department of Public Health told The Times. For the week that ended May 30 — the most recent available — viral levels in wastewater rose by 13% versus a comparable period several weeks earlier.

In addition, there is a slight increase in the rate in which COVID surveillance tests are turning up positive in L.A. County. For the most recent week, 5% of COVID surveillance tests showed positive results for infection, up from 3.8% in early May. COVID-related visits to the emergency room remain low in Los Angeles County.

There were still low rates of COVID-19 illness in San Francisco, the local Department of Public Health said.

Yet coronavirus levels in wastewater in Northern California’s most populous county, Santa Clara County, are starting to increase, “just as they have over past summers,” the local Public Health Department said in an email to The Times. As of Friday, coronavirus levels in the sewershed of San José was considered “high.” Viral levels were “medium” in Palo Alto and “low” in Sunnyvale. Nimbus is the most common subvariant in the county.

Across California, coronavirus levels in wastewater are at a “medium” level; the last time viral levels were consistently “low” was in April, according to the state Department of Public Health’s website.

“Future seasonal increases in disease levels are likely,” the California Department of Public Health said in an email to The Times Friday.

The uptick in COVID comes as many medical professional organizations and some state and local health officials are objecting to the Trump administration’s recent moves on vaccine policy, which some experts fear will make it more difficult for people to get vaccinated against COVID-19 and other diseases.

Federal officials in May weakened the CDC’s official recommendations from recommending the COVID vaccine to everyone age 6 months and up. The CDC now offers “no guidance” on whether healthy pregnant women should get the COVID vaccine, and now asks that parents of healthy children talk with a healthcare provider before asking that their kids get inoculated.

The American College of Obstetricians and Gynecologists issued a rebuke of the changing vaccine recommendations for pregnant women, accusing the U.S. Department of Health and Human Services — led by the vaccine-skeptic secretary, Robert F. Kennedy Jr. — of “propagating misinformation.” The American Pharmacists Assn. wrote that dropping the vaccine recommendation for pregnant women did “not appear to be based on the scientific evidence provided over the last few years.”

And an open letter by 30 organizations specializing in health — including the American Medical Assn. — said that “we must continue to prioritize high levels of COVID-19 vaccine coverage in pregnant patients to protect them and their infants after birth.”

Chin-Hong said he recommends pregnant women get vaccinated “one million percent.”

“The data are incredibly clear that pregnant women do have a higher rate of complications, hospitalization and premature births when they did not get vaccinated [against COVID] compared to the ones that did,” said Dr. Yvonne Maldonado, an infectious-disease expert at Stanford University. The vaccines also help newborns, as antibodies generated by the mom-to-be cross the placenta, and can protect the newborn for a certain number of months, she said.

That’s essential protection, given that newborns can’t be vaccinated under 6 months of age, Maldonado said. If newborns are infected, they have relatively high rates of hospitalization — as high as those age 65 and over, Maldonado said.

Then, last week, Kennedy abruptly fired all members of a highly influential committee that advises the CDC on vaccine policy. In an op-ed to the Wall Street Journal, Kennedy criticized the previous members of the Advisory Committee on Immunization Practices, founded in 1964, as being “plagued with persistent conflicts of interest and has become little more than a rubber stamp for any vaccine.”

Maldonado, a professor in pediatric infectious diseases and epidemiology, was one of the fired vaccine advisors. She called their mass dismissal unprecedented in the history of the ACIP.

“We are absolutely in uncharted territory here,” Maldonado said. “I think it’s going to be really hard to understand what vaccines are going to go forward. … They’re also going to review the entire vaccination schedule.”

In general, routine review of vaccine schedules are a good thing, and prior reviews have concluded that the current recommended shots are safe and effective, Maldonado said. But the criteria being circulated by recently appointed federal officials “could actually wind up refusing to recommend, say, measles vaccine or HPV vaccine, because I’ve seen some of the misinformation that has been out there about some of these vaccines. …

“And if any of that is accepted as truth, we could wind up losing some of these vaccines,” Maldonado said.

“The question, then, is: ‘Would those vaccines disappear?’ … Hard to know,” she said. But it’s also possible that federal officials could begin to stop paying for certain vaccines to be administered to children of low-income families.

She rejected Kennedy’s characterization of the committee as a rubber stamp for vaccine makers. “Generally, a decision to not pursue a vaccine happens usually well before anything gets to a vote,” Maldonado said.

A joint statement by the governors of California, Oregon and Washington condemned Kennedy’s dismissal of the vaccine advisors as “deeply troubling for the health of the nation” and defended the fired vaccine advisors as having been “carefully screened for major conflicts of interest.”

“We have grave concerns about the integrity and transparency of upcoming federal vaccine recommendations and will continue to collaborate to ensure that science and sound medicine prevail to prevent any loss of life,” Gov. Gavin Newsom said in a statement Thursday.

Traditionally, the advisory committee’s recommendations on who should get vaccinated were adopted by the director of the CDC.

“It was one of the most depressing weeks in American health … a dark period for everyone right now, and demoralizing,” said Chin-Hong, of UC San Francisco. “It’s very destabilizing.”

The American Academy of Pediatrics called the purge of the vaccine advisors “an escalating effort by the administration to silence independent medical expertise and stoke distrust in lifesaving vaccines.” Kennedy’s handpicked replacements include people known for their criticism of vaccines, the Associated Press reported.

The mass firing “likely puts vaccine access and insurance coverage at serious risk,” the L.A. County Department of Public Health said in a statement. “It corrodes trust in the recommended schedule for vaccines, not only by the public, but by medical providers who rely on the ACIP for science-based, apolitical guidance.”

The departments of public health for California, Oregon and Washington said they “continue to recommend all individuals age 6 months and older should have access and the choice to receive currently authorized COVID-19 vaccines, with an emphasis on protecting higher risk individuals, such as infants and toddlers, pregnant individuals, and others with risks for serious disease.”

The L.A. County Department of Public Health said in a statement that, “at this time in Los Angeles County, current vaccine recommendations for persons aged 6 months and older to receive the COVID-19 vaccine remain in effect and insurance coverage for COVID-19 vaccines is still in place.”