The World Health Organization is now listing four SARS-CoV-2 variants of concern (VOC) and seven additional variants of interest (VOI) worldwide (www.who.int/en/activities/tracking-SARS-CoV-2-variants/). A VOC is characterized by an increase in transmissibility or virulence, a change in clinical presentation, and/or decreased effectiveness of vaccines or therapeutics. A VOI is a strain that has caused multiple case clusters.
WHO has also adopted a new nomenclature based on the Greek alphabet. The four VOCs are Alpha (UK or Kent variant, B.1.1.7); Beta (South Africa variant, B.1.351); Gamma (Brazil variant, P.1); and Delta (India variant, B.1.617.2).
Of emerging concern are VOIs detected in the U.S. (Epsilon, B.1.427/B.1.429; and Iota, B.1.526); Brazil (Zeta, P.2); multiple countries (Eta, B.1.525); the Philippines (Theta, P.3); India (Kappa, B.1.617.1, a variant of Delta); and Peru (Lambda, C.37).
Recent attention has focussed on the Delta variant, which was flagged as a VOC in April 2021. The variant harbours two mutations in the receptor binding domain of the spike protein, which may enhance cell entry and transmissibility. Three sub-lineages have been identified: B.1.617.1 (now called Kappa), B.1.617.2 (Delta) and B.1.617.3 (unnamed). Little is known about sub-lineages 1 and 3.
Delta (sub-lineage 2) has demonstrated increased transmission in the U.K and has largely supplanted the Alpha (B.1.1.7) variant. As of 2 June, B.1.617.2 was believed to be the dominant strain for new COVID-19 patients in that country with over 42,000 probable/confirmed cases identified to date (www.gov.uk/government/publications/covid-19-variants-genomically-confirmed-case-numbers/variants-distribution-of-case-data-11-june-2021). A German study reported that the variant was resistant to bamlanivimab and had moderate efficacy in evading host antibodies induced by prior infection or vaccination (Hoffmann et al. bioRxiv, 5 May 2020; www.biorxiv.org/content/10.1101/2021.05.04.442663v1).
Health Canada lists the Delta variant as a VOC but has not yet provided data on the number of cases. B.1.617 cases (all three sub-lineages) have been reported in all provinces and one territory. Most cases identified in March and April were sub-lineage 1 (Kappa); most cases identified at the border have been sub-lineage 2 (Delta).
Preliminary data suggest that current COVID-19 vaccines are effective against the Delta variant. An analysis using the EAVE II surveillance platform in Scotland (1 April to 6 June) reported that Delta cases occurred in all age groups but were more common than the Alpha variant in children aged 6-9 years (Sheikh et al. Lancet 2021; epublished 14 June 2021; www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01358-1/fulltext). The Delta variant was also associated with an increased risk of hospitalization (hazard ratio 1.85 vs. Alpha cases). However, hospitalization rates were similarly low for both variants in vaccinated individuals.
After two doses of the Pfizer-BioNTech vaccine, the effectiveness, defined as preventing CoV-2 infection, was estimated to be 92% against the Alpha variant and 79% against the Delta variant. With two doses of the AstraZeneca vaccine, the effectiveness was estimated to be 73% against the Alpha variant and 60% against the Delta variant.