A highly transmissible variant of the SARS-CoV-2 virus originally from the United Kingdom is emerging rapidly in the United States, with 76 cases detected in 12 states when this report was filed.

The mutated strains do not appear more virulent, but the enhanced transmission narrows the margin of error for breaks in personal protective equipment and other exposures in the community and healthcare settings.

The Centers for Disease Control and Prevention (CDC) held a Dec. 30, 2020, press conference to update the rapidly evolving situation.

“Health officials in the United Kingdom and South Africa recently reported two new variants of the SARS-CoV-2 virus,” said Henry Walke, MD, incident manager for the CDC’s COVID-19 response. “Both appear to infect people more easily. It is important to know that at this time there is no evidence that either of these variants causes more severe disease or increases the risk of death.”

The B117 UK variant has undergone multiple changes, including “a mutation in the receptor binding domain (RBD) of the spike protein,” the CDC reports. This mutation apparently allows the spike protein of the virus to bind more easily to cells to enhance transmission.

“Currently there is no evidence to suggest that the variant has any impact on the severity of disease or vaccine efficacy,” the CDC emphasized.

Thirty-Two Cases in California

Cases of the U.K. variant have been reported in California (32), Colorado (4), Connecticut (2), Florida (22), Georgia (1), Indiana (1), Maryland (2), Minnesota (5), New York (4), Pennsylvania (1), Texas (1), and Wisconsin (1). The South African variant had not been detected in the United States when this report was filed.

“Because the variants spread more rapidly, they could lead to more cases and put even more strain on our heavily burdened healthcare systems,” Walke said. The variant first seen in the United Kingdom — which is now spreading among people with no travel history in the United States — is 56% more transmissible than the original pandemic coronavirus, researchers report in a paper under review.1

“As a result of this increased transmissibility, existing control measures are likely to be less effective, and countries may require stronger proactive interventions to achieve the same level of control,” they concluded. “We found no evidence that the new variant is associated with higher disease severity, but without strengthened controls, there is a clear risk that future epidemic waves may be larger — and hence associated with greater burden — than previous waves.”

A lot remains unknown, including whether the variant in South Africa is spreading within the United States. “Based on our present knowledge, experts believe our current vaccines will be effective against these strains,” Walke said. “We’re still learning how these variants might respond to drugs and other COVID-19 treatments, including monoclonal antibodies and convalescent plasma.”

Greg Armstrong, MD, director of the CDC Office of Advanced Molecular Detection, also weighed in on the vaccine efficacy issue.

“From what we know from experience with this mutation and other mutations is that it’s unlikely to have a large impact on vaccine-induced immunity or on an existing immunity from previous strains,” he said. “It may cause a small impact, but keep in mind that it’s likely that the amount of immunity that is induced by either natural infection or by vaccination is great enough that [variant infection] may not have any noticeable effect at all.”

The CDC is rapidly expanding a national surveillance system to collect and genetically sequence SARS-CoV-2 strains in the United States to identify variant strains. “We anticipate scaling up to 3,500 whole genome sequences per week,” Armstrong said. “This is a consortium of over 160 groups around the (United States) that are doing sequencing. It includes public health, academia, nongovernmental organizations, and industry.”

The virus likely would need to accumulate multiple mutations in the spike protein to evade immunity induced by vaccines or by natural infection, the CDC states.2

“Among these possibilities, the last — the ability to evade vaccine-induced immunity — would likely be the most concerning because once a large proportion of the population is vaccinated, there will be immune pressure that could favor and accelerate emergence of such variants by selecting for ‘escape mutants,’” the CDC concludes. “There is no evidence that this is occurring, and most experts believe escape mutants are unlikely to emerge because of the nature of the virus.”


  1. Davies NG, Barnard RC, Jarvis CI, et al. Estimated transmissibility and severity of novel SARS-CoV-2 variant of concern 202012/01 in England. https://cmmid.github.io/topics/covid19/reports/uk-novel-variant/2020_12_23_Transmissibility_and_severity_of_VOC_202012_01_in_England.pdf
  2. Centers for Disease Control and Prevention. Emerging SARS-CoV-2 variants. Updated Jan. 15, 2021. https://www.cdc.gov/coronavirus/2019-ncov/more/science-and-research/scientific-brief-emerging-variants.html