Alpha, Beta, Delta, Gamma: What's Important to Know About SARS-Cov
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NEWS Alpha, Beta, Delta, Gamma: What’s important to know about SARS-CoV-2 variants of concern? n Cite as: CMAJ 2021 July 12;193:E1059-60. doi: 10.1503/cmaj.1095949 Posted on cmajnews.com on June 18, 2020 he World Health Organization recently announced a new nam- ing system for SARS-CoV-2 vari- Tants using the Greek alphabet. The new naming system is aimed at preventing people from referring to the variants by the country where they were first detected. Four of these variants of con- cern — Alpha, Beta, Delta and Gamma — have spread to most provinces and territories in Canada. Alpha (B.1.1.7) The Alpha strain is the most common variant of concern in Canada, accounting for more than 216 000 cases of COVID-19 across the country as of June 17. First documented in the United Kingdom in September last year, Alpha is 50% more transmissible than earlier Image copyright iStock.com/Ergin Yalcin. No standalone file use permitted. strains and was a major driver of Canada’s Canada’s COVID-19 strategy may need to change in light of cases and deaths linked with the highly third wave of COVID-19 in the first transmissible Delta variant. months of 2021. The Alpha variant is also linked with Delta (B.1.617.2) COVID-19 cases in that province as of June surges in COVID-19 cases and hospitaliza- First documented in India in October last 14. Alberta has reported several hundred tions among young people — although it’s year, the highly transmissible Delta vari- cases and officials say the number of cases unclear whether those surges were due to ant is on track to eclipse the Alpha vari- appears to be doubling every six to 12 days. the variant or other factors, says Dr. Gerald ant as Canada’s dominant strain this Both Alberta and Manitoba have reported Evans, chair of infectious diseases at summer. deaths linked to the Delta variant, includ- Queen’s University in Kingston, Ont. Studies out of the United Kingdom sug- ing the death of at least one person who Daily reports from Public Health gest the Delta variant is up to 60% more was fully vaccinated against COVID-19. Ontario suggest new cases from the Alpha transmissible than the Alpha variant. Vaccines appear to be less effective variant are declining. Evans attributes Experts have warned the Delta strain may against the Delta variant than the Alpha this drop to more than half of Canadians drive a fourth wave of COVID-19 in Canada strain, but they are still highly effective at receiving at least one dose of a COVID- and are urging governments to shift the preventing disease after two doses. 19 vaccine. focus of vaccination campaigns to deliver One study found that two doses of the One study found that the AstraZeneca second doses as soon as possible. Pfizer vaccine were 88% effective against vaccine was 70% effective in preventing According to Evans, Canada’s case symptomatic disease from the Delta symptomatic COVID-19 caused by the counts involving the Delta variant are variant, versus 93% effective against the Alpha variant, while another study unclear because the variant may not be Alpha strain. Two doses of the AstraZeneca estimated the efficacy of the Pfizer detected by some rapid tests. Ontario esti- were 60% effective against Delta com- vaccine at roughly 90%. mates Delta accounted for 40% of new pared to 66% against Alpha. © 2021 CMA Joule Inc. or its licensors CMAJ | JULY 12, 2021 | VOLUME 193 | ISSUE 27 E1059 However, both vaccines were only 33% In one study, researchers found that be 1.7–2.4 times more transmissible than effective against Delta after one dose, ver- two doses of the Pfizer vaccine were 75% other local strains in that country. Canada sus 50% effective against Alpha. effective against any infection from the has reported more than 15 000 cases to Meanwhile, a preprint study reported Beta variant, and 89.5% effective against date. high levels of protection when it came any infection from the Alpha variant. How- The Gamma variant has some of the to hospitalizations for COVID-19. The ever, vaccine effectiveness against severe same mutations in its spike protein as the Pfizer vaccine was 94% effective against or fatal disease from either the Alpha or Alpha and Beta strains, which allow it to NEWS hospitalizations from the Delta or Alpha Beta variants was very high at 97.4%. attach more easily to human cells. How- variants after one dose and 96% effective Novavax clinical trials showed 89% ever, “it’s not anywhere near as transmis- after two doses. The AstraZeneca vaccine efficacy in the United Kingdom, compared sible as Alpha or Delta,” says Evans. was 71% effective against hospitalizations to just 60% in South Africa, where the Previous infection with SARS-CoV-2 after one dose and 92% effective after two. Beta strain was common. Similarly, trials appears to provide less protection against According to Chief Public Health Offi- of the Johnson & Johnson vaccine reinfection with the Gamma variant than cer, Dr. Theresa Tam, Canada may need to reported lower levels of protection other strains. However, at least one preprint adjust COVID-19 vaccination targets to against moderate to severe COVID-19 in study showed that the Gamma variant is account for the Delta variant. Models that South Africa than in the United States. less resistant to antibody responses from indicated that Canada could begin easing Meanwhile, South Africa stopped plans previous illness or vaccination than the pandemic restrictions when 75% of to rollout the AstraZeneca vaccine because Beta variant. people had at least one dose of a COVID- clinical trials did not show protection Evidence also suggests that the Gamma 19 vaccine did not account for the Delta against mild or moderate illness caused by variant struggles to compete with other strain. the Beta variant. strains in the wild. In a pre-print study, Still, Canada is in a good position to Recent studies suggest that mutations Italian researchers tracked the concurrent curb the spread of the Delta variant, says in the Beta variant’s spike protein might spread of Alpha and Gamma variants and Evans. “Because of our vaccine strategy allow it to escape the immune response found that the Alpha variant became to get one dose into everybody, the trained by vaccines. increasingly common while the Gamma amount of SARS-CoV-2 circulating is really “Everybody was worried about Beta variant did not. low,” he explains. As such, the Delta vari- especially because there’s this vaccine ant “is not getting a good opportunity to escape issue,” says Evans. “If it was Diana Duong, CMAJ surge forward.” [more] transmissible like Alpha, we would Content licence: This is an Open Access article have been in trouble, but it isn’t. It seems distributed in accordance with the terms of the Beta (B.1.351) to be no more transmissible [than early Creative Commons Attribution (CC BY-NC-ND First documented in South Africa in May strains of the virus].” To date, Canada has 4.0) licence, which permits use, distribution and 2020, the Beta variant was linked with documented more than 1900 cases. reproduction in any medium, provided that the increases in hospitalizations and deaths original publication is properly cited, the use is noncommercial (i.e., research or educational during that country’s second wave. Gamma (P.1) use), and no modifications or adaptations are Vaccines also appear to be less effective in The Gamma variant, first documented in made. See: https://creativecommons.org/ preventing COVID-19 from the Beta variant. Brazil in November 2020, is estimated to licenses/by-nc-nd/4.0/ E1060 CMAJ | JULY 12, 2021 | VOLUME 193 | ISSUE 27 .