Will Coronavirus Variants Soon Dominate in U.S.?

The SARS-CoV-2 variant first documented in Britain could become the primary strain in the U.S. by March, researchers found.

Despite only 76 infections with the variant, B.1.1.7 or VOC 202012/01, detected in the U.S. through Jan. 13, models predict it will crowd out other strains and become the most common cause of COVID-19 by March, according to Summer Galloway, PhD, of the CDC, and colleagues, writing in Morbidity and Mortality Weekly Report.

In addition to public health measures, they warned "enhanced genomic surveillance" will be necessary to track its spread.

This variant is more transmissible, thanks to multiple genetic mutations, including in the S protein receptor-binding domain, they said. Not only is the virus more transmissible, but it may cause false negative results on COVID-19 diagnostic testing via PCR assays, and could be less susceptible to neutralizing antibodies, such as monoclonal antibody therapy and convalescent plasma.

Last week, the FDA alerted clinicians to the possibility of false negative results on certain molecular tests targeting only a single region of the virus' genome.

Mutations in the variant cause S-gene target failure (SGTF) on at least one PCR-based assay, which Britain used as a proxy for identifying cases with the new variant, and offered a preview for the U.S. based on their epidemiological data.

"U.K. regions with a higher proportion of B.1.1.7 sequences had faster epidemic growth than did other areas, diagnoses with SGTF increased faster than did non-SGTF diagnoses in the same areas, and a higher proportion of contacts were infected by index patients with B.1.1.7 infections than by index patients infected with other variants," Galloway and colleagues wrote.

The group then modeled U.S. data, based on current prevalence of the variant at an estimated <0.5% of U.S. cases, as well as immunity from previous infection at 10%-30%, a time-varying reproductive number for current variants, and incidence of an estimated 60 cases per 100,000 cases per day on Jan. 1.

They found prevalence of the variant "initially low," but with rapid growth in early 2021 until it becomes the dominant variant in March, regardless of whether transmission of the variant is increasing or decreasing.

And the current vaccination campaign won't corral the new strain right away. With 1 million doses administered today and 95% efficacy against infection 14 days after completing the two-dose course, the models showed no change in early epidemic trajectories. After the variant becomes dominant, however, its "transmission was substantially reduced." (This assumes the vaccines prevent infection, which has yet to be demonstrated.)

Galloway and colleagues also said that while B.1.1.7 hasn't been associated with more severe clinical outcomes, continued genomic surveillance is needed to track variants of concern. In addition, vaccination coverage must be higher than anticipated to achieve the same level of population-level disease control versus less transmissible variants, they said.

The researchers noted that no infections with either the South African variant dubbed B.1.351, or the Brazilian/Japanese variant known as P.1 -- both of which are also believed to be extra-transmissible -- have been confirmed in the U.S. to date.

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