Canadian Medical Association

illustration of SARS-CoV-2 cell

Experts have detected many SARS-CoV-2 variants since the beginning of the pandemic. Three in particular have raised concerns about enhanced transmissibility, effects on immunity, reduced efficacy of therapeutic agents and reducing the accuracy of diagnostic testing.

Members of the DynaMed editorial team share what you need to know about the SARS-CoV-2 variants and their clinical impact.

This information is accurate as of February 11,2021.


The first SARS-CoV-2 variant, which carried a spike protein amino acid substitution D614G, emerged early in the pandemic. By June 2020, the D614G variant replaced the original strain to become the dominant circulating strain globally. Another variant known as B.1.1.7 was detected in September in the United Kingdom. By December it was flagged as a “variant of concern” because it was quickly becoming the dominant variant in the London area, and as of January 31, 2021, it has been detected in 80 countries, including the United States.

The B.1.1.7 variant has 14 lineage-defining mutations including a few in the spike protein that appear to confer higher binding affinity to the cellular receptor. A third variant know as the B.1.351 lineage was detected in South Africa in October and another called B.1.1.28 was first detected in travelers from Brazil in January 2021 (this variant has since been renamed P.1 lineage). Some of the same spike mutations have evolved spontaneously in these distinct SARS-CoV-2 variant strains, suggesting that immunologic pressure may have provoked similar selection of these variants.

Are they more transmissible?

It is becoming clear that that these particular SARS-CoV-2 variants increase transmissibility of the virus. Genetic surveillance and modeling studies estimate the B.1.1.7 variant to be 50 to 75 percent more transmissible. Further, while lockdowns stifled transmission of previous SARS-CoV-2 strains, infection control measures were less effective at blocking the spread of B.1.1.7 in the U.K. The mechanisms by which different mutations confer a selective advantage of these variants is an area of intense investigation.

Are they deadlier?

Despite some reporting to the contrary in the mainstream press, there is no evidence to-date that any of these SARS-CoV-2 variants are associated with more severe COVID-19 or death. A technical briefing from the Scientific Advisory Board for Emergencies (SAGE) in the U.K. reported preliminary findings from unpublished analyses suggesting potentially increased risk of death associated with the B.1.1.7 variant. However, without access to the primary data set and methods, we are unable to independently confirm these conclusions.

Will SARS-CoV-2 vaccines provide immunity?

In terms of the efficacy of vaccines against these SARS-CoV-2 variants, a few recent studies reveal some insights. In a preprint (non-peer reviewed) study with 20 volunteers who received two doses of Pfizer/BioNTech (n = six) or Moderna (n = 14) vaccines, both mRNA vaccines elicited antibodies capable of neutralizing SARS-CoV-2 variants. However, plasma from vaccinated people was less effective at neutralizing variants with specific mutations, a finding similarly observed in a preprint study from Moderna that showed a six-fold reduction in antibodies able to neutralize the B.1.351 variant. Despite lower neutralizing antibody titers, it is expected that the vaccines still elicit protective immunity against the current SARS-CoV-2 variants. Moderna is also investigating the benefit of a booster dose of vaccine directed against variants.

It’s hard to predict the clinical impact of these and future SARS-CoV-2 variant strains. As we exert more immunologic pressure on the virus due to increasing rates of natural- and vaccine-acquired immunity, we may find different variants than those discovered today. Broad genetic surveillance will be necessary to monitor for variants and track their clinical impact.

For more information, see the topic COVID-19 (Novel Coronavirus) in DynaMed. 

Original article published on EBSCO Health Notes. Written by:

  • Vito Iacoviello, MD, Deputy Editor for Infectious Disease, Allergy, and Immunology at DynaMed; and
  • Heather D. Marshall, PhD, Senior Medical Writer in Infectious Disease, Allergy, and Immunology and Digital Media Specialist at DynaMed.

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This material is for informational purposes only. It is not intended to be a substitute for professional medical advice and should not be relied on as health or personal advice. The opinions stated by the authors are made in a personal capacity and do not necessarily reflect those of the Canadian Medical Association and its subsidiaries including Joule. 

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