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Newest Omicron Covid-19 lineages gaining ground in United States

We’re still in the Age of Omicron, but the face of it keeps changing.

The United States appears to be in the midst of another biological baton pass between Covid-19 variants. The Omicron lineage BA.2 and its spinoff, BA.2.12.1, drove cases this spring, building into waves of infections in places like the Northeast and parts of California. Now, two other forms of Omicron, BA.4 and BA.5, are eating into the BA.2 group’s dominance.

More than 1 in 5 Covid-19 infections last week were caused by BA.4 and BA.5, according to updated estimates posted Tuesday by the Centers for Disease Control and Prevention. That’s up from 13% the week prior. The rest of the cases are from the BA.2 lineages.

BA.4 and BA.5 are picking up speed because they’re able to evade the body’s antibody response even more so than other variants, meaning they’re very good at establishing infections in people who have some level of protection. “Overall, this raises concerns about more frequent BA.4/BA.5 vaccine breakthrough infections than for BA.1/BA.2, and for Omicron reinfections,” the European Centre for Disease Prevention and Control wrote in an update this week. People who were infected by an earlier Omicron version could be susceptible to an infection from BA.4 or BA.5 not long after they recover, scientists have found, though the combination of vaccination and an earlier Omicron infection provides more durable protection than an infection alone.

Related: The ‘five pandemics’ driving 1 million U.S. Covid deaths

But even as the body’s ability to block infection is weakened in the face of the newer variants, protection against more serious outcomes continues to be maintained for most people who’ve been vaccinated or had prior infections. As of now, BA.4 and BA.5 do not seem to cause more severe disease on average compared to other forms of Omicron.

The newer lineages are emerging in the United States as the country’s average daily infection count seems to have plateaued at just over 100,000 (which, with at-home tests, rolled-back testing programs, and people forgoing tests because their infections are so mild, is a major undercount).

So how will BA.4 and BA.5 affect the landscape? Better transmitting variants, as we all know by now, add weight to the side of the scale that promotes increased spread. But factors on the other side of the scale can act as a drag on transmission — all the recent infections that people have had, for example, and perhaps a seasonal boost in parts of the country where people are spending more time outside.

The toll of the variants could look different based on region. The Northeast is past the peak of its BA.2.12.1 spike, but “we’re at the beginning of seeing the impact of BA.4/5,” Jacob Lemieux, an infectious diseases physician at Massachusetts General Hospital, told reporters last week. Perhaps the ascendance of the two latest subvariants will just slow down the pace of the region’s decline in infections. But other places, particularly areas of the country that didn’t have substantial BA.2 waves, could be more ripe for spikes in infections.

Already, transmission has been picking up in areas including parts of Florida and New Mexico. The South experienced devastating infection waves the past two summers, likely in part because people headed indoors to escape the heat, and experts are watching to see if the region again sees a summertime surge.

According to the latest CDC data, the region with the highest prevalence of BA.4 and BA.5 at this point — at more than 30% — is the one including Texas, New Mexico, Arkansas, Oklahoma, and Louisiana.

Of course, thanks to the levels of population immunity, the danger of Covid cases has changed over time, with infections far less likely to lead to hospitalizations and deaths. But while the individual risk is lower, experts argue that total infections still matter — particularly when they’re numbering in the hundreds of thousands a day.

Mild cases can still be disruptive to people’s lives. Even vaccinated people seem vulnerable to long Covid, if at lower rates than unvaccinated people. And some of those infections will still lead to hospitalizations and deaths, whether it was someone who was unvaccinated or — perhaps because they’re older, have other health conditions, or haven’t kept up with boosters — who did not get as robust protection from the shots. As it is, some 300 people in the United States are still dying from Covid a day.

Experts trying to gauge what BA.4 and BA.5 could do in the United States have been looking at other countries’ experiences with the lineages. South Africa had a sizable wave of infections driven by BA.4 and BA.5, though a much smaller one than its initial Omicron wave (which was caused by a subvariant called BA.1). While deaths in South Africa increased, it was to a much smaller extent.

But in Portugal, where BA.5 is dominant, deaths are now on par with where they were during its initial Omicron wave (though deaths are much lower than during the country’s waves during the pre-vaccine era). The increase in hospitalizations in Portugal has occurred mainly in people 60 and over, according to the ECDC.

“The growth advantage reported for BA.4 and BA.5 suggest that these variants will become dominant” in Europe, the agency wrote, “probably resulting in an increase in Covid-19 cases in the coming weeks.”


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