Why BA.4 and BA.5 pose big coronavirus risk to California

July 5, 2022 Updated 1:25 PM PT

Are people in your life being infected with the coronavirus, even after being caught up in an earlier wave?

You aren’t alone. For the third straight year, the arrival of summer has brought fresh uncertainties about the COVID-19 outlook in California.

The latest development upending the pandemic landscape is the growing dominance of two subvariants — BA.5 and, to a lesser degree, BA.4 — that not only are ultra-contagious but have shown the ability to reinfect those who contracted earlier Omicron strains.

This combination of initial and recurring infectivity carries enormous implications. Here’s what we know:

How common are BA.4 and BA.5?

According to the latest figures from the U.S. Centers for Disease Control and Prevention, BA.5 comprised an estimated 53.6% of new cases nationwide for the weeklong period that ended Saturday. This completes a stunning rise to dominance for the subvariant, which only a month ago was thought to be responsible for a bit less than 10% of new cases.

Over the week ending Saturday, BA.4 accounted for an estimated 16.5% of new cases — making it the third-most-common Omicron strain in circulation, behind only BA.5 and BA.2.12.1.

The estimated viral proportions are similar in the southwestern U.S., which includes California, Arizona, Nevada, Hawaii and U.S. Pacific territories.

What are the concerns with BA.4 and BA.5?

Both subvariants are highly contagious. The worry is that trait, combined with their apparent reinfection prowess, could prolong or exacerbate California’s already months-old coronavirus wave.

Of particular concern is BA.5. Dr. Eric Topol, director of the Scripps Research Translational Institute in La Jolla, recently called it “the worst version of the virus that we’ve seen.”

“It takes immune escape, already extensive, to the next level, and, as a function of that, enhanced transmissibility, well beyond Omicron (BA.1) and other Omicron family variants that we’ve seen,” he wrote in a blog post.

Omicron has spawned a number of subvariants since emerging late last fall, and those have largely been characterized by ramped-up infectivity. But “BA.5 is a different beast with a new superpower: Enough alteration in the spike protein that immunity from either prior vax or prior Omicron infection (including recent infection) doesn’t offer much protection,” according to Dr. Robert Wachter, chair of UC San Francisco’s Department of Medicine.

“As BA.5 becomes the dominant U.S. variant, its behavior will determine our fate for the next few months, until it either burns itself out by infecting so many people or is replaced by a variant that’s even better at infecting people,” Wachter wrote Sunday on Twitter. “Neither is a joyful scenario.”

Among the biggest repercussions of BA.5, he added, is that “prior infection — including an Omicron infection as recent as last month — no longer provides robust protection from reinfection.”

“That old saw about hybrid immunity (vax plus infection) providing ‘immunity superpower,’ and thus no need to be careful, is no longer true,” he wrote. “We’re seeing such folks get reinfected within 1 to 2 months.”

Can BA.4 and BA.5 make you sicker?

In an epidemiological update released last month, the World Health Organization noted that current available evidence doesn’t indicate a change in disease severity associated with either. However, the agency also said their growing prevalence “has coincided with a rise in cases” in several regions, with those increases leading to a surge in hospitalizations in some countries.

BA.5, Topol said, “led to a marked rise in hospitalizations in Portugal where it rapidly became dominant,” and is having a similar effect in many European nations and Israel.

There have been reports that a wave fueled by BA.4 and BA.5 in South Africa was associated with somewhat lower death rates than its first Omicron waves.

What about vaccines?

One major question is whether the potential rollout of an Omicron-specific booster later this year will help combat the rise of BA.4 and BA.5. Given how much the variant has mutated in the last seven months, there are concerns such an offering may be relatively outdated by the time it’s available.

In the meantime, officials and experts alike say getting vaccinated and boosted, when eligible, continues to provide strong protection against the worst health impacts of COVID-19.

According to the latest available data from the California Department of Public Health, unvaccinated individuals were more than five times more likely to get COVID-19 than their vaccinated-and-boosted counterparts. They were also 7.5 times more likely to be hospitalized and 14.5 times more likely to die from the disease.

“Vax/boost remains hugely valuable in preventing a severe case that might lead to hospital/death,” Wachter wrote. “But its value in preventing a case of COVID, or preventing transmission, is now far less than it once was.”

Where does California stand?

According to the most recent data, California recorded a 12% increase in coronavirus cases compared with mid-June, tallying an average of more than 16,900 per day over week ending Thursday, according to data compiled by The Times. On a per capita basis, that’s 303 cases a week for every 100,000 residents.

Two-thirds of the state’s counties are now in the high COVID-19 community level, in which the CDC recommends universal masking in indoor public spaces.

“With the continued increase in cases, and now as you’re seeing the corresponding increase in hospitalizations … we’re really worried,” L.A. County Public Health Director Barbara Ferrer said last week.

“Our case numbers, they are staying pretty high,” Ferrer said. And she expressed concern about the rising numbers of even more contagious Omicron subvariants, BA.4 and BA.5, at a time when more people have lowered their guard and shed their masks.

So far, Los Angeles County health officials have not imposed new masking rules. But they have warned that might be necessary, perhaps later in July, if new coronavirus-positive hospitalizations continue to rise.

“It seems clear that BA.5 will lead to an ongoing plateau, if not a moderate surge, lasting through summer and into fall,” Wachter wrote. “Beyond that, much depends on whether a new variant emerges to supplant it. Given the pattern of the past year, it would be foolish to bet against that.”

How do you protect yourself?

VACCINES: Residents looking to stave off the worst health impacts of COVID-19, officials say, should also get vaccinated if they haven’t already — and get a first and/or second booster when eligible. Residents who are at least 50 years old, as well as those 12 and older who are immunocompromised, became eligible in March for a second booster four months after their first.

MASKS: While masks are not required in indoor public places, many experts say they can be a good idea. California officials have consistently urged residents to use face coverings in public interior settings — including stores, restaurants, theaters and family entertainment centers. Los Angeles County has gone a step further and still requires face coverings on public transit, including ride-sharing vehicles, and in indoor transportation hubs.

CHOICES: Outdoors gatherings are preferable to indoors. If you must gather inside, make the setting as well-ventilated as possible by opening doors and windows, if possible. Wearing masks also offers an additional layer of protection, officials say.

TESTING: Officials recommend using rapid tests to check infection status as close to the start of a gathering as possible — especially if older people or those with underlying health conditions are present, or if attendees have frequent contact with vulnerable people.