There is a new variant of omicron dominating the United States. It could pose the biggest threat to immunity yet.

A new version of omicron dominates in the United States

The coronavirus subvariant known as BA.5 accounted for nearly 54% of the country’s Covid cases on Saturday, according to the Centers for Disease Control and Prevention. A similar sub-variant, BA.4, is 17% more.

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

Both subvariants also seem to evade 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 omicron variant as the dominant version of the coronavirus in the United States in April.

Francois Balloux, director of University College London Genetics Institute, said this was likely another reason subvariants took over.

“At this point now, I think all of these variants are actually about equally transmissible, so there’s not a huge difference,” he said. “It’s just that some are slightly better at infecting people who have been vaccinated or infected with previous variants.

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

Pfizer told NBC News it may have an updated vaccine targeting BA.4 and BA.5 ready for distribution in October.

The most common symptoms of BA.4 and BA.5

In the UK, where BA.4 and BA.5 also account for the majority of new Covid cases, the most common Covid symptoms in the past week were runny nose, sore throat, headache, persistent cough and fatigue. Less than a third of respondents reported fevers, according to data from the Zoe COVID Symptom Study, which asks people to self-report their symptoms via smartphone apps.

This matches symptoms reported in the UK in the spring, when the BA.2 subvariant was dominant.

Balloux said that no difference has been observed so far between the BA.4 or BA.5 symptoms and those of the 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 quite different,” he said, so cross-protection “isn’t as good.”

Balloux added, however, that “BA.2, BA.4 and B.5 from a neutralizing antibody perspective are essentially interchangeable.” This could mean that people infected with BA.2 now have some protection.

Montefiori said BA.4 and BA.5 were also not found to cause more severe disease.

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

On the contrary, the increase in cases and hospitalizations observed in some places are more likely related to the decrease in vaccine protection.

“We now have waning immunity in people who were boosted six months 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 be available in early to mid-fall.

“Companies are now rushing to manufacture the vaccine containing BA.4/BA.5 and clinically test it,” Montefiori said.

But experts have pointed out that there may not be a dramatic difference in protection between additional boosters of current vaccines and specific omicron injections. Current vaccines still work well to prevent serious illness and death.

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

For that reason, he added, people eligible for a second booster — those over 50 or those with compromised immune systems — might not want to wait.

“If it’s been more than six months since your last boost, you might want to consider getting boosted again now with the current vaccine to keep your protection strong while we’re still going through this pandemic,” Montefiori said.

Also, Balloux said, it’s hard to predict whether BA.5 will still be dominant later this year.

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

Europe and South Africa preview the sequel

The number of reported Covid cases has remained relatively stable in the United States since May, but the number of cases is increasing around the world.

By the end of June, new weekly cases had increased by 32% in Southeast Asia, 33% in Europe and 47% in the region comprising 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 omicron cases worldwide, while BA.4 accounted for 12%.

South Africa has seen an increase in cases caused by BA.4 and BA.5 this spring, and Covid hospitalizations are increasing in the UK. Experts said the trends likely indicate the virus is getting better at reinfecting people and evading vaccine protection.

Yet the future of the pandemic will depend not only on the properties of the variants, but also on human behavior and the degree of immunity that has built up in the population.

“People tend to overestimate how much the virus has changed very recently,” Balloux said. “There was a massive, massive change between delta and omicron, and then there was, again, a pretty massive 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 another major shift in the evolution of the virus could yet occur.

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

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