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SAN FRANCISCO, Calif. (KRON) — COVID-19 variants keep getting sneakier at slipping past vaccines and natural immunity – meet the latest, evasive forms of the virus: two omicron subvariants, BA.4 and BA.5, which now make up a majority of COVID-19 cases around the U.S.

Even if you were infected by omicron during last winter’s surge, you can still be re-infected by BA.4 or BA.5 this summer, said Dr. Peter Chin-Hong, a UC San Francisco infectious disease expert.

“The superpower of BA.4 and BA.5 is, if you had omicron in January, you’re still going to be susceptible to getting BA.4 and BA.5. It’s the escape artist of COVID, the Houdini, because the spike protein looks so different, even (compared) to BA.1. The front guards, the antibodies, are not recognizing it,” Chin-Hong explained.

Chin-Hong stressed that even though vaccines are not 100% effective at preventing infections, they are very effective for fighting off the virus to prevent it from causing serious illnesses in most people.

“Even though (currently available vaccines) are not necessarily great right now at preventing the enemy at the front gate, when the enemy gets inside, it’s going to kick it out and you’re not going to go to the hospital,” Chin-Hong said.

Dr. Bob Wachter, chair of UCSF’s Department of Medicine, said BA.5 is destined to be the dominant strain.

That’s bad news, especially considering how immune-evasive the strain’s genetic mutations are.

“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 doesn’t offer much protection,” Wachter wrote on Twitter.

Eric Topol, a professor of molecular medicine, said BA.5 is the “worst version of the virus that we’ve seen.”

Topol explained on Twitter, “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 (including BA.1.1, BA.2, BA.2.12.1, and BA.4).”

The BA.5 subvariant first popped up as a dominant strain in South Africa, and now has been detected throughout the world.

Pandemic fatigue has lowered people’s willingness to wear masks and practice social distancing this summer.

“Mandates are gone – likely forever in most of the U.S. And most people have ditched their masks and are unlikely to put them back on, no matter how large the surge. So it’s up to each of us to determine our own risk tolerance, and then own behavior,” Wachter wrote.

Chin-Hong, Wachter, and Topol all agree that boosters are the best lines of defense to prevent a surge in COVID-related hospitalizations. A new booster aimed at omicron will be available this fall.

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

According to Topol, “The big question now is whether an Omicron booster, directed to BA.1, will help when that variant is no longer with us, and we will be close to 100% BA.5 within a matter of weeks. And no doubt there will be further troublesome variants that lie ahead, be they more in the Omicron family or in a whole new lineage.”