New subvariants better at evading immune protection

A new version of ommicron is dominant in the US

According to the Centers for Disease Control and Prevention, the coronavirus sub-variant known as BA.5 was responsible for nearly 54% of Covid cases in the country as of Saturday. A comparable sub-variant, BA.4, makes up 17% more.

“They’re taking over, so obviously they’re more contagious than previous variants of omicron,” said David Montefiori, a professor at the Human Vaccine Institute at Duke University Medical Center.

The two subvariants also seem to escape protection from vaccines and previous infections more easily than most of their predecessors.

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 vaccine antibodies than BA.2, which replaced the ommicron variant in April as the dominant version of the coronavirus in the US.

Francois Balloux, the director of the University College London Genetics Institute, said this is most likely another reason why the subvariants have taken over.

“At this stage, I think all of these variants are actually about equally transferable, so there’s not a huge difference,” he said. “Some are only slightly better at infecting people who have been vaccinated or infected by previous variants.”

A Food and Drug Administration advisory last week recommended modifying the upcoming booster shots from Pfizer and Moderna to target BA.4 and BA.5 directly.

Pfizer has told NBC News it may 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 UK, where BA.4 and BA.5 are also responsible 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 a third of people surveyed reported a fever, according to data from the Zoe COVID Symptom Study, which asks people to self-report their symptoms via smartphone apps.

That is consistent with the symptoms reported in the UK in the spring, when the BA.2 subvariant was dominant.

Balloux said no difference has so far been observed between BA.4 or BA.5 symptoms and those of previous subvariants. But people infected with the original version of the omicron variant over the winter may be susceptible to the newer sub-variants.

“BA.1 and BA.2 are quite different,” he said, so the crotch protection “isn’t that great.”

However, Balloux added that “BA.2, BA.4 and B.5 are essentially interchangeable from a neutralizing antibody perspective.” That could mean that people who got BA.2 infections now have some protection.

Montefiori said BA.4 and BA.5 have also not been found to cause more serious diseases.

“There’s really no clear evidence that they are more or less likely to make people sick and cause serious illness and death,” he said.

Rather, increases in the number of cases and hospitalizations seen in some places have more to do with declining vaccine protection.

“We now have waning immunity in the people who were boosted six months or more ago,” Montefiori said.

Do we need more booster shots, and when?

The FDA estimates that ommicron-specific boosters from Pfizer and Moderna will be available in early to mid-fall.

“The companies are now rushing to make the BA.4/BA.5-containing vaccine and test it clinically,” Montefiori said.

But experts stressed that there may not be a dramatic difference in protection between extra boosts of current vaccines and ommicron-specific shots. Current vaccines still work well to prevent serious illness and death.

“The virus is moving in a direction of escaping our vaccines more and more, but it hasn’t found a way to escape the vaccines to a really significant degree,” Montefiori said.

For that reason, he added, people who qualify for second boosters — people over 50 or immunocompromised — may not want to wait.

“If your last boost was more than six months ago, you might want to consider boosting again now with the current vaccine to keep your protection strong while we’re still weathering this pandemic,” Montefiori said.

In addition, Balloux said, it’s hard to predict whether BA.5 will still dominate later this year.

“Given the uncertainty, there is no right or wrong,” he said. “There are only compromises.”

Europe and South Africa offer a taste of what comes next

The number of reported Covid cases has remained relatively flat in the US since May, but the number of cases is increasing worldwide.

By the end of June, new weekly cases were up 32% in Southeast Asia, 33% in Europe and 47% in the region that includes the Middle East, Central Asia, North Africa and the Horn of Africa, according to the World Health Organization. As of June 19, BA.5 accounted for 43% of ommicron cases worldwide, while BA.4 accounted for 12%.

South Africa saw an increase in cases caused by BA.4 and BA.5 this spring, and Covid hospitalizations in the UK are on the rise.

Still, the future of the pandemic will depend not only on the traits of variants, but also on human behavior and how much immunity has built up in the population.

“People tend to overestimate how much the virus has changed very recently,” Balloux said. “There was a huge, huge change between delta and omicron, and then there was another pretty huge change between BA.1 and BA.2.”

That’s not quite the case with BA.4 and BA.5, he said, although he noted that there could be another big shift in the virus’s evolution.

“I’m not saying it won’t happen,” he said.

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