Omicron BA.5: One variant to rule them all…for now

Today, the more infectious Omicron BA.5 subvariant is officially the dominant strain of Covid in the United States. – who himself had been behind cases for about a month.

After the original Omicron variant appeared on American shores late last year and caused the deadliest wave of the pandemic, a succession of Omicron sub-variants 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 accounted for just 9.6% of cases in the United States, while its predecessor BA.2.12.1 topped the heap at 62%. Today, the CDC estimates that the subvariant is responsible for about 54% of new cases here. This is double BA.2.12.1, which now accounts for 27% of infections. The rise in power of BA.5 also leaves the sister sub-variant BA.4 in the dust at 16%. It’s a faster climb than any other variant during the pandemic. And there have been many.

CDC

One of the reasons why BA.5 is so dominant is that it appears 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 did not have the same impact.

“The BA.5 subvariant of Omicron is the worst version of the virus we’ve seen,” said Eric Topal, founder and director of the Scripps Research Translational Institute, professor of molecular medicine and executive vice president of Scripps. Research, in a sub-stack article last week. “It takes the already extensive immune evasion to the next level and, depending on that, improves transmissibility, well beyond Omicron (BA.1) and other variants of the Omicron family that we have. views.”

In other words, BA.5 is much better at evading vaccine-provided immunity and particularly good at evading immunity conferred by previous infection.

For example, BA.4 and BA.5 have recently resulted in a substantial increase in South Africa which has not been affected by the county’s high level of immunity.

According to the journal Nature, those with “hybrid immunity” from vaccination and past infection are less able to ward off BA.4 or BA.5 than they were previous strains. This is because the vaccines we have now target the spike proteins of the previous strains. And the new variants have very different mutations.

Although vaccines are less effective, they are and remain more effective than vaccination by infection. The bites also help people infected with BA.4 and BA.5 better ward off the most unpleasant effects of the virus.

While cases have remained fairly static in the United States, The New York Times notes that this may be more the result of the measuring stick than the actual measurement. The document reports that with local and federal reductions in testing services, “PCR lab testing capacity in July will be only half of what it was in March.” Add to that the increased use of home tests, the results of which are generally not reported, and virus surveillance across the country is significantly reduced from what it was even six months ago.

Hospitalizations and deaths also did not increase significantly, but in Portugal it took three weeks after the BA.5 peak in cases for deaths to peak.

A more potent ability to re-infect also means BA.5 has a larger pool of potential carriers. While other variants are limited by the protection afforded by inoculation, BA.5 can recur in populations that assume they are more protected than they actually are.

“BA.4/5 has resulted in a substantial surge of cases in South Africa, regardless of their high levels of immunity,” Kaitlyn Jetelina observed about two weeks ago. Jetelina tweets and blogs as Your Local Epidemiologist.

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

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

What does this mean for the United States?

Our future is harder to predict based on the experiences of other countries than it was before. Portugal was much harder hit than the United States in the Delta wave of winter 2000-2001 and less hard hit by last winter’s Omicron surge, which ravaged the United States. This could be good for us, as the original Omicron is probably more closely related than Delta to BA. 5. Previous Omicron infections may provide more protection. Our winter wave from Omicron was also newer, which helps. But Portugal has a higher recall rate than the United States

One thing is certain: this will not be the last variant we will see.

Topol warns that “new versions of the virus…are accelerating and we are not done yet, far from it”.

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

A new strain known as BA.5.1 caused the biggest outbreak of cases in Macau last week, prompting local authorities to bring much of the region under lockdown.

BA.5.1 appeared in the United States in small numbers, as well as in the United Kingdom and Portugal. The strain has been described as “the daughter of BA.5”, and Christine Pagel, professor and head of the Clinical Operations Research Unit at University College London, wrote in an article last month that “it seems that BA.5 and 5.1 will probably win”. become the global dominant variants.

Since then, however, BA.2.75 has raised its head. Although not yet in the United States, the BA.2 subvariant has been detected in England, Germany and India, where it was reportedly found in 18% of samples. And it spreads fast. See table below for graph of its growth in India.

More, unfortunately, to come.


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