What is BA.4.6? The CDC is tracking a new COVID ‘variant of concern’ that’s overtaking earlier Omicron strains in at least 4 U.S. states

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New lineages of the Omicron COVID variant, like BA.4 and BA.5, are helping spark a wave of reinfections, as people who previously caught COVID-19 contract COVID again.

Now, the U.S. Centers for Disease Control and Prevention (CDC) is tracking a new “variant of concern”: BA.4.6. This week, the CDC included the BA.4 spinoff in its weekly tracking of COVID cases, with the agency’s chief data officer tweeting that the new subvariant had actually been “circulating for several weeks” in the U.S. The CDC designates strains as “variants of concern” if it displays greater transmissibility, reduced effectiveness of treatment, increased severity, or decreased neutralization by antibodies.

According to the CDC, BA.4.6 made up 4.1% of COVID cases for the week ending July 30. The new variant is more prevalent in the region comprised of Iowa, Kansas, Missouri, and Nebraska, where it makes up 10.7% of local cases. The mid-Atlantic region and the South are also seeing rates of BA.4.6 above the national average.

The new strain has also been detected in 43 other countries, according to outbreak.info, a community repository of COVID information. 

BA.5, which one epidemiologist called “the worst version of the virus that we’ve seen” due to its increased transmissibility and ability to evade existing immunity, is still dominant in the U.S., making up 85.5% of all COVID cases as of July 30. BA.4 and BA.5 are responsible for driving a global surge in COVID cases, including in places that had held off the virus until the current wave, like the Chinese city of Macau. 

As of now, there isn’t much data as to whether BA.4.6 is better than BA.4 or BA.5 at evading immunity. Eric Topol, founder and director of the Scripps Research Translational Institute, tweeted on Tuesday that BA.4.6.s mutation “does not appear to be concerning [compared to] BA.4/5″ with only a handful of new mutations compared to the earlier subvariants.

Omicron-specific vaccines

Even if BA.4.6. isn’t significantly worse than existing strains, the speed at which new variants of concern are emerging is alarming public health officials who are planning for new vaccine boosters this fall.

On Friday, the U.S. Food and Drug Administration said that it would seek to approve boosters that directly target the BA.5 variant this autumn, rather than make more Americans eligible or a second booster based on the original 2020 strain of COVID. Currently, only Americans over age 50 are eligible for a second booster. 

But new variants might make still-in-development boosters less effective by the time they’re finally ready. Dr. Anthony Fauci, the White House’s chief medical advisor, said the new boosters are trying to hit a “moving target” when it came to determining which variants to tackle.

The White House is now pushing for universal coronavirus vaccines that can target multiple variants at once. “These are vaccines that are going to be far more durable, that are going to provide far longer-lasting protection, no matter what the virus does or how it evolves,” Ashish Jha, the White House COVID-19 response coordinator, told Stat News after a July 25 summit on COVID vaccines.

Yet even with new vaccines on the way, experts say that Americans eligible for another booster should get one now, as opposed to waiting for a more tailored shot to come in the fall. A study published Tuesday found that a second booster cut the rate of breakthrough infections by 65% among Israeli health care workers.