The FDA recommended that Covid vaccine makers target two omicron subvariants — BA.4 and BA.5 — in new booster shots expected to come this fall.
A new version of omicron is dominant in the U.S.
The coronavirus subvariant known as BA.5 accounted for nearly 54% of the country’s Covid cases as of Saturday, according to the Centers for Disease Control and Prevention. A similar subvariant, BA.4, makes up 17% more.
“They’re taking over, so clearly they’re more contagious than earlier variants of omicron,” said David Montefiori, a professor at the Human Vaccine Institute at Duke University Medical Center.
The two subvariants also appear to evade protection from vaccines and previous infections more easily than most of their predecessors.
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Montefiori estimated that BA.4 and BA.5 are about three times less sensitive to neutralizing antibodies from existing Covid vaccines than the original version of the omicron variant, BA.1. Other research suggests that BA.4 and BA.5 are four times more resistant to antibodies from vaccines than BA.2, which replaced the omicron variant as the U.S.’s dominant version of the coronavirus in April.
Francois Balloux, the director of the University College London Genetics Institute, said that’s most likely another reason the subvariants have taken over.
“At this stage now, I think all these variants actually are roughly equally transmissible, so there’s not a huge difference,” he said.”It’s just some are slightly better at infecting people who have been vaccinated or infected by previous variants.”
The Food and Drug Administration last week recommended modifying coming booster shots from Pfizer and Moderna to target BA.4 and BA.5 directly.
Pfizer has told NBC News that it could have an updated vaccine targeting BA.4 and BA.5 ready to be distributed in October.
The most common symptoms of BA.4 and BA.5
In the U.K., where BA.4 and BA.5 also account for the majority of new Covid cases, the most common Covid symptoms last week were runny nose, sore throat, headache, persistent cough and fatigue. Less than one-third of people surveyed reported fevers, according to data from the Zoe COVID Symptom Study, which asks people to self-report their symptoms through smartphone apps.
That’s consistent with the symptoms reported in the U.K. in the spring, when the BA.2 subvariant was dominant.
Balloux said no difference has been observed so far between BA.4 or BA.5 symptoms and those of previous subvariants. But people who were infected with the original version of the omicron variant during the winter may be susceptible to the newer subvariants.
“BA.1 and BA.2 are pretty different,” he said, so the cross-protection “is not as great.”
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Balloux added, though, that “BA.2, BA.4 and B.5 from a neutralizing antibody perspective are essentially interchangeable.” That might mean that people who got BA.2 infections have some protection now.
Montefiori said BA.4 and BA.5 also haven’t been found to cause more severe disease.
“There’s really no clear evidence that they’re more or less likely to make people sick and cause severe illness and death,” he said.
Rather, rises in cases and hospitalizations observed in some places more likely have to do with fading vaccine protection.
“We have waning immunity now in the people who got boosted half a year or more ago,” Montefiori said.
Will we need more booster shots, and when?
The FDA estimates that omicron-specific boosters from Pfizer and Moderna will become available in early to mid-fall.