By Jennifer Kearney-Strouse
At a Thursday afternoon session at Internal Medicine Meeting 2021: Virtual Experience, CDC director Rochelle Walensky, MD, MPH, FACP, offered attendees an update on some variants of SARS-CoV-2 currently circulating in the U.S.
"There's two areas where we're looking," Dr. Walensky said. "There's variants of interest and variants of concern."
A variant of interest, she explained, is one with genetic markers that have been associated with changes to receptor binding, reduced neutralization by antibodies generated against previous infection or vaccination, potential diagnostic impact, reduced treatment efficacy, or a predicted increase in transmissibility or disease severity. "It's really more in vitro, in vivo data," Dr. Walensky said. In variants of concern, there is evidence of increased transmissibility, more severe disease, significant reduction in neutralization, reduced treatment or vaccine effectiveness, or diagnostic detection failures, she said.
The main variants of concern in the U.S. right now are B.1.1.7, first identified in the United Kingdom; B.1.351, identified in South Africa; B.1.427 and B.1.429, both from California; and P.1, from Brazil. The B.1.1.7 variant has increased transmissibility (of about 50%), is likely to increase severity of disease, and has about a twofold decrease in neutralization by vaccines, according to convalescent or postvaccination sera, Dr. Walensky said. The B.1.351 variant is associated with a 50% increase in transmissibility and a sixfold decrease in neutralization. "However, we still believe that this is enough neutralization for the vaccine to work," she said.
The two California variants have a 20% increase in transmissibility, a potential increase in severity of disease, and a twofold reduction in neutralization, while the P.1 variant from Brazil has 150% increased transmissibility with a similar reduction in neutralization. "We're following these all very, very carefully, and partially because of this increased transmissibility we've been concerned about," Dr. Walensky said.
In January, the CDC recognized that the B.1.1.7 variant, which had quickly become the dominant variant in the U.K., had emerged in the United States in September 2020. "Our modelers at CDC had demonstrated that the B.1.1.7 had the potential to increase the U.S. pandemic trajectory," she said. "The increased transmissibility of 1.1.7 warranted universal and increased compliance with mitigation strategies. We were very worried about this, especially with the winter surge."
The CDC has increased genomic surveillance and sequencing, Dr. Walensky explained. "We've been able to scale that up dramatically, both in partnerships with private labs, as well as with our public health labs and academic partnerships," she said. "We're now sequencing somewhere between 25,000 to 30,000 sequences a week, and this past week, we sequenced about 8.8% of all virus that was newly detected. What we then do is we can tell you how much of what variant is out there."
The CDC has analyzed sequencing data through April 10 and found that about 55% of all virus sequences in the U.S. are now variant B.1.1.7. In most regions of the U.S., B.1.1.7 is currently the dominant variant.
The remaining question is whether B.1.1.7 is more deadly, Dr. Walensky said. She pointed to a study from England, published by Nature on March 15, that looked at 2,245,263 positive SARS-CoV-2 tests in the community and 17,452 COVID-19-associated deaths between Nov. 1, 2020, and Feb. 14, 2021. The researchers were able to determine the presence or absence of B.1.1.7 in 51% of the tests and found a marked split in patients' survival curves between the B.1.1.7 and non-B.1.1.7 variant.
But the absolute difference may be minuscule, Dr. Walensky noted. "Yes, there's a statistical difference between them, but it probably is not [a] clinically meaningful difference, because people with SARS tend to do pretty well until you get to the higher age categories," she said. ■