This is a summary, written by members of the CITF Secretariat, of:

Curran J, Dol J, Boulos L, Somerville M, McCulloch H, MacDonald M, LeBlanc J, Barrett L, Hatchette T, Comeau J, Reynolds B, Shin D, Gallant A, Wong H, Crowther D, Yu Z. Transmission characteristics of SARS-CoV-2 variants of concern rapid scoping review. medRxiv. April 2021. doi: 10.1101/2021.04.23.21255515.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A rapid scoping review highlighting the transmission characteristics of SARS-CoV-2 variants of concern (VOCs) was prepared by the Nova Scotia COVID-END Evidence Synthesis Group on behalf of the SPOR Evidence Alliance, which included CITF-funded investigator Dr. Lisa Barrett. The authors explore relevant questions, such as what criteria are used to define a new VOC, how much more transmissible are these VOCs, and why?

Main conclusions:

  • Authors found risk of transmission of the B.1.1.7 variant, reported in 15 studies, was 45-71% higher than non-VOCs.
  • Looking at potential mechanisms of transmission, aspects such as increased viral load, immune evasion and increased ACE2 binding by the virus were suggested, but a definitive mechanism for enhanced transmission is still unclear.

The authors evaluated the three SARS-CoV-2 variants of concern identified as of March 2021 (B.1.1.7, B.1.351 and P.1). They suggested that variants of concern should have three characteristics; 1- they should be phylogenetically distinct from other SARS-CoV-2 variants, 2- they contain mutations of biological significance, and 3- they are capable of spreading rapidly, with dominance and/or selective advantage over other variants. They retrieved almost 1800 articles and analyzed 16 papers and seven other literature sources, including government reports, policy statements, and pre-print articles.

The authors found that risk of transmission of the B.1.1.7 variant, reported in 15 studies, was 45-71% higher than non-VOCs. R0 value for B.1.1.7, defined as the expected number of subsequent SARS-CoV-2 positive cases generated by one infected individual, was found to be 75-78% higher than other previously circulating SARS-CoV-2 viruses. Interestingly, the authors were not able to find sufficient evidence implicating similarly increased transmission risk of B.1.35.1 and P.1 variants.

They also evaluated 12 studies that discussed potential mechanisms of transmission by these VOCs. While aspects such as increased viral load, immune evasion and increased ACE2 binding by the virus were suggested, a definitive mechanism for enhanced transmission is still unclear. Finally, the authors recommended that decision-makers should continue to monitor VOCs and emerging evidence on this topic to inform public health policy.