More transmissible variants of the SARS-CoV-2 virus are emerging globally and had been detected in three U.S. states as 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 as healthcare workers begin to take their first doses of the COVID-19 vaccines.

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

“Health officials in the United Kingdom and South Africa recently reported two new variants of SARS CoV-2,” 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.”1

The B117 U.K. variant has undergone multiple mutations, some apparently allowing the spike protein of the virus to bind more easily to cells to enhance transmission.

Bad News for Swamped Healthcare

Urging more vigilance with masks, social distancing, and hand hygiene, Walke cited the risk that an increase in cases due to heightened transmissibility could hit a healthcare system that is running on the thinnest of margins in many areas.

“Because the variants spread more rapidly, they could lead to more cases and put even more strain on our heavily burdened healthcare systems,” he said.

The variant first seen in the U.K. — which is now spreading among people in the United States with no travel history — is 56% more transmissible than the original pandemic coronavirus, researchers reported in a paper under review.2 Some models have suggested a higher transmissibility than that, with estimates in the range of 70%.

“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,” the researchers 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.”

The U.K. variant likely has circulated there since September 2020, Walke said. The second variant was first identified in South Africa and has been circulating there since October 2020.

“This second variant developed independently of the first variant,” he said. “Both variants have been detected in other countries.”

The first case with the U.K. variant recently was identified in Colorado. “The lack of reported travel history suggests that this variant has been transmitted from person to person in the United States,” Walke said. “The arrival of this variant in the U.S. was expected, considering how widespread it is in the U.K. and how frequently people travel between the U.S. and the U.K. The evidence to date indicates that both newly emerging variants spread more easily and quickly than other strains.”

Vaccines Should Work

A lot remains unknown, including whether the variant in South Africa is spreading within the United States. It had not been detected in the United States as this report was filed.

“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.”

Gregory 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,” Armstrong 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.”1

The CDC is expanding a national surveillance system rapidly to collect and genetically sequence SARS-CoV-2 strains in the U.S. 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 U.S. that are doing sequencing. It includes public health, academia, nongovernmental organizations, and industry.”


  1. Centers for Disease Control and Prevention. Transcript: CDC update on COVID-19. Dec. 30, 2020.
  2. Davies NG, Barnard RC, Jarvis CI, et al. Estimated transmissibility and severity of novel SARS-CoV-2 variant of concern 202012/01 in England. Dec. 23, 2020. Paper in pre-review.