BA.5's fast rise to dominance: 5 things to know about the omicron subvariant

The omicron subvariant BA.5 is quickly gaining prevalence in the U.S. and now accounts for nearly 54 percent of all cases, according to the CDC's latest variant proportion update for the week ending July 2. 

On June 25, CDC estimates showed the strain accounted for about 37 percent of cases. It's closely related to omicron subvariant BA.4, which is estimated to account for nearly 17 percent of cases. BA.4 and BA.5 have become known as "sister variants" since they were first discovered in South Africa last winter. Collectively, they make up 70 percent of U.S. cases, estimates show. 

Experts for months had predicted BA.5 would become dominant, pointing to how the strain made larger week-by-week jumps than earlier variants that went on to become dominant. On June 4, estimates showed BA.5 accounted for just 7.6 percent of U.S. cases. 

Four more things to know about BA.5: 

1. It's particularly good at evading immunity from vaccination and prior infection. Researchers from Beth Israel Deaconess Medical Center in Boston recently found neutralizing antibody responses against BA.4 and BA.5 were twentyfold lower than against the original omicron strain. Such findings help explain why they've spread faster than other omicron relatives and indicate the potential for reinfections to become more common, The Wall Street Journal reports. The variant's dominance also comes as more Americans have dropped public health measures, such as masking, and as many people experience a natural waning of vaccine protection, both of which may contribute to the subvariant's rapid spread. 

"The omicron subvariant BA.5 is the worst version of the virus that we've seen," Eric Topol, MD, founder and director of the Scripps Research Translational Institute in San Diego, wrote in a June 27 blog post. "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."

2. BA.5 may prolong the national rise in COVID-19 cases. COVID-19 cases hit record levels in January amid the omicron surge, with a seven-day average of more than 800,000, and consistently fell nationwide through March, CDC data shows. Cases rose steadily throughout April and May as other highly transmissible omicron subvariants spread nationwide and remained elevated through June. 

Public health experts told the Journal that BA.5's increased prevalence in the U.S. will, at the very least, prolong the national uptick in cases. As of July 4, the nation's seven-day case average was 105,754, a 10 percent increase in the last 14 days, according to data tracked by The New York Times. 

3. There is not much evidence BA.5 causes more severe disease. BA.5 and BA.4 fueled a surge in cases and hospitalizations in South Africa this spring, despite 90 percent of the population having some immunity against the virus. However, the country did not see a sharp rise in deaths accompanying this surge, and the wave was not as high as previous COVID-19 waves, according to the Times.

4. The FDA has instructed vaccine makers to retool COVID-19 shots to target BA.4 and BA.5. The need to update the vaccine is growing more urgent by the day, scientists told the Times, citing rising case counts fueled by the highly transmissible subvariants, loosening public health precautions and the natural waning of vaccine protection. Vaccine makers are working to finalize and manufacture the shots in time for a fall booster campaign.

"Omicron is so different that, to me, it seems pretty clear we're starting to run out of ground in terms of how well these vaccines protect against symptomatic infections," Deepta Bhattacharya, PhD, an immunologist at the University of Arizona in Tucson, told the Times. "It's very important that we update the shots."


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