Today, the more infectious Omicron subvariant BA.5 is officially the dominant Covid strain in the U.S. Until then, BA.5 was tied with its sister Omicron subvariant, BA.4, as both steadily outcompeted BA.2.12.1 — which in itself has been leading cases for the last month or so.
After the original Omicron variant hit US shores late last year and caused the deadliest wave of the pandemic, a series 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 26 February. Less than a month ago, on June 4, it accounted for just 9.6% of US cases, while predecessor BA.2.12.1 topped the heap with 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 of BA.5 also leaves sister sub-variant BA.4 in the dust by 16%. That’s a faster climb than any other option over the course of the pandemic. And there were a lot of them.
CDC
One of the reasons BA.5 is so dominant is that it appears to be more transferable than even BA.2.12.1 — (BA.4 has some of the same key peak protein mutations as BA.5, but did not have the same impact.
“The Omicron BA.5 subvariant is the worst version of the virus we’ve seen,” Eric Topal, who is founder and director of the Scripps Research Translational Institute, professor of molecular medicine and executive vice president of Scripps Research, said in a post on substack last week. “It takes immune rescue, which is already extensive, to the next level and, as a function of that, improved transmissibility, far beyond Omicron (BA.1) and other variants of the Omicron family that we have seen.”
In other words, BA.5 is much better at avoiding immunity provided by vaccines, and especially good at avoiding immunity provided by a previous infection.
For example, BA.4 and BA.5 led to a significant surge in South Africa recently, which was not affected by the high level of immunity in the county.
According to the journal Nature, those who have “hybrid immunity” from vaccination and past infection are less able to ward off BA.4 or BA.5 than the previous strains. This is because the vaccines we have now target the peak proteins of previous strains. And the new variants have some very different mutations.
Although vaccines are less effective, they are still more effective than immunization through infection. The jabs also help those infected with BA.4 and BA.5 better ward off the worst effects of the virus.
Although cases remain fairly static in the US, the New York Times notes that this may be more a result of the measuring stick than the actual measurement. The paper reported that with local and federal cutbacks in testing services, “capacity for lab-based PCR testing 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 usually not reported, and virus surveillance across the country is greatly reduced from what it was even six months ago.
Hospitalizations and deaths also did not increase significantly, but then in Portugal it took three weeks after the BA.5 peak in cases to peak in deaths.
The stronger 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 work its way back through populations that assume they are more protected than they really are.
“BA.4/5 has led to a significant wave of cases in South Africa, despite their high level of immunity,” Caitlin Jetelina noted about two weeks ago. Jetelina tweets and blogs under the pseudonym Your Local Epidemiologist.
She continues by noting that “in South Africa, the BA.4/5 wave contributed to excess deaths, but less than previous waves.”
In Europe, Portugal is the country most affected by the new Omicron sub-variants. Cases peaked on May 16, according to the World Health Organization. Deaths in that country peaked almost exactly three weeks later, on June 6.
What does this mean for the US?
Our future is harder to predict based on the experience of other countries than it used to be. Portugal was hit much harder than the US in the Delta wave winter of 2000-2001 and less so by the Omicron wave last winter that ravaged the US. This may be fine for us, as the original Omicron is probably more closely related to BA than Delta. 5. Previous infections with Omicron may provide more protection. Our Omicron winter wave was also more recent, which helps. But Portugal has a higher booster rate than the US
One thing’s for sure: 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 means.”
Indeed, like tropical storms in the Caribbean this summer, there are a number of new options already on the way. And experts say significant mutations — especially in the Omicron subvariants — are coming at an increasing rate.
A new strain known as BA.5.1 caused the largest outbreak of cases in Macau last week, prompting local authorities to place much of the region under lockdown.
The BA.5.1 appeared in the US in small numbers, as well as in the UK and Portugal. The strain has been described as “the daughter of BA.5,” and Christine Pagel, professor and director of the Department of Clinical Operations Research at University College London, wrote in an article last month that “it appears that BA.5 and 5.1 are likely to win to become the overall dominant options.’
Since then, however, BA.2.75 has reared its head. Although not yet in the US, the BA.2 subvariant has been found in England, Germany and India, where it was reportedly found in 18% of samples. And it spreads fast. See the chart below for its growth graph in India.
More, unfortunately, to come.
Here’s the latest picture for the new BA.2.75 subline (alias: “Centaurus”) – an evolutionary leap from the BA.2.
It is most commonly found in India, showing extremely rapid growth up to 18% of recent samples.
Also spreading rapidly to other countries.🧵 pic.twitter.com/JnkLsU9Lnw
— Mike Honey (@Mike_Honey_) July 2, 2022
Add Comment