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Today, the more-infectious Omicron BA.5 subvariant is officially the dominant Covid strain in the U.S. Up until how, BA.5 has been tied to its sister Omicron subvariant, BA.4, as both had steadily outcompeted BA.2.12.1 — which itself had been driving cases for the past month or so.

After the original Omicron variant appeared on U.S. shores late last year and caused the deadliest wave of the pandemic, a succession of Omicron subvariants have come and gone: BA.1.1, BA.2, BA.2.12.1 and now BA.4 and BA.5.

BA.5 was first identified in South Africa on February 26. Less than a month ago, on June 4, it only accounted for 9.6% of cases in the U.S., while predecessor BA.2.12.1 sat atop the heap at 62%. Today, the CDC estimates the subvarient is responsible for about 54% of new cases here. That’s double BA.2.12.1, which now accounts for 27% of infections. BA.5’s rise also leaves sister subvariant BA.4 in the dust at 16%. It’s a faster ascention than that of any other variant over the course of the pandemic. And there’ve been a lot of them.

One reason BA.5 is so dominant is that it seems to be more transmissible than even BA.2.12.1 — (BA.4 has some of the same key spike protein mutations as BA.5, but hasn’t had the same impact.

“The Omicron sub-variant BA.5 is the worst version of the virus that we’ve seen,” said Eric Topal, who is Founder and Director of the Scripps Research Translational Institute, Professor of Molecular Medicine and Executive Vice-President of Scripps Research, in a substack post last week. “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.”

In other words, BA.5 is much better at evading the immunity provided by vaccines and especially good at dodging the immunity conferred by previous infection.

For example, BA.4 and BA.5 drove a substantial surge in South Africa recently that was not impacted by the county’s high level of immunity.

Per the journal Nature, those who have “hybrid immunity” from vaccination and a past infection are less able to ward off the BA.4 or BA.5 than they were previous strains. That’s because the vaccines we have now are targeting the spike proteins of previous strains. And the new variants have some very different mutations.

While vaccines are less effective, they’re and still more effective than immunization through infection. The jabs also help those infected with BA.4 and BA.5 better ward off the virus’s nastiest effects.

While cases have remained fairly static across the U.S., the New York Times notes that that may be more a result of the measuring stick than the actual measurement. The paper reports that with local and federal cuts to testing services, “lab-based P.C.R. testing capacity in July will be only half of what it was in March.” Add to that the increased use of at-home tests, the results of which are generally not reported, and virus surveillance across the nation is greatly reduced from what it was even six months ago.

Hospitalizations and deaths have not risen meaningfully, either, but then in Portugal it took three weeks after the BA.5 peak in cases for deaths to peak.

A more potent ability to reinfect also means that BA.5 has a larger pool of potential carriers. While other variants are limited by the protection afforded by inoculation, BA.5 can make its way back through populations who assume they’re more protected than they actually are.

“BA.4/5 drove a substantial case wave in South Africa regardless of their high level of immunity,” observed Kaitlyn Jetelina about two weeks ago. Jetelina tweets and blogs under the moniker Your Local Epidemiologist.

She goes on to note that “in South Africa, the BA.4/5 wave contributed to excess deaths, but fewer than past waves.”

In Europe, Portugal is the country hardest hit by the new Omicron subvariants. It experienced a peak in cases on May 16, according to the World Health Organization. Deaths in that country peaked almost exactly three weeks later, on June 6.

What does that mean for the U.S.?

Our future is harder to predict based on other countries’ experiences than it was previously. Portugal got hit much harder than the States in the winter 2000-2001 Delta wave and less hard by last winter’s Omicron surge, which ravaged the U.S. That might be good for us, since the original Omicron is likely more closely related than Delta to BA.5. Previous Omicron infections may provide more protection. Our winter Omicron wave was more recent, as well, which helps. But Portugal has a higher booster rate than the U.S.

One thing is for certain: This won’t be the last variant we see.

Topol warns that “new versions of the virus…are accelerating and we’re not done yet, by any stretch.”

Indeed, like tropical storms in the Caribbean this summer, there is a line of new variants already on their way. And experts say significant mutations — especially in the Omicron subvariants — are coming with increasing speed.

A new strain known as BA.5.1 caused the largest outbreak of cases ever in Macau last week, which prompted local officials to put a large swath of the region under lockdown.

BA.5.1 has turned up in the U.S. in small numbers, as well as the U.K. and Portugal. The strain has been described as “the daughter of BA.5,” and Christine Pagel, Professor and Director of University College London’s Clinical Operational Research Unit, wrote in a piece last month that “it looks like BA.5 and 5.1 will likely win out to become the overall dominant variants.”

Since then, however, BA.2.75 has reared its head. While it’s not in the U.S. yet, the subvariant of BA.2 has been detected in England, Germany and India, where it reportedly has been found in 18% of samples. And it’s spreading fast. See chart below for graph of its growth in India.

More, unfortunately, to come.

Here’s the latest picture for the new BA.2.75 sub-lineage (nickname: “Centaurus”) – an evolutionary jump from BA.2.

It has most commonly been detected in India, showing extremely rapid growth to 18% of recent samples.

It is also spreading rapidly to other countries.
🧵 pic.twitter.com/JnkLsU9Lnw

— Mike Honey (@Mike_Honey_) July 2, 2022