The emergence of so-called “worrying” variants at the end of 2020 marked a turning point in the Covid-19 pandemic, the term thus entering everyone’s vocabulary. The acceleration in the world of one of them, the Delta variant, raises questions about its origin, transmissibility, hot spots and potential for resistance to the vaccine.
What is a variant?
Through genome sequencing, we can determine the specific order of individual genes and nucleotides that make up DNA and RNA. If you think of the virus as a book, it is as if all the pages have been cut into pieces. Sequencing allows us to put words and sentences back in the right order. The variants differ from each other depending on the mutations. Thus, two copies of the book would be “variants” if one or more of the cut pieces were different.
It should also be noted that variants appeared throughout the pandemic without this having any effect on viral behavior. However, the emergence of variants of concern, where mutations led to a change in the characteristics of the virus (increased transmission and severity of the disease, reduced efficacy of vaccines, failed screening) had important consequences. .
The emergence and transmission of B.1.1.7 (Alpha), B.1.351 (Beta) and P.1 (Gamma) in Canada have given rise to third waves of transmission which have resulted in overloading of health care systems health and new restrictions. The World Health Organization introduced a new naming system, based on the Greek alphabet, for coronavirus variants in spring 2021.
What is the Delta variant, and where did it emerge?
The Delta variant is a variant of concern also known as B.1.617.2 and is one of three known sublines of B.1.617. According to the United States Centers for Disease Control and Prevention, the Delta variant was first detected in India in December 2020.
One of the characteristics of the Delta variant is its increased transmissibility, with estimated increases of 40 to 60% compared to the Alpha variant. Recent data from Scotland suggests that the risk of hospitalization doubles following infection with the Delta variant (compared to the Alpha variant), especially in people with at least five other health problems. An increased risk of hospitalization has been observed from data collected in England.
Epidemiological analysis, which looks at things such as the distribution of infection and the severity of the disease, can often provide rapid assessments of changes in the characteristics of the virus. Studying specific mutations using structure-to-activity relationship analysis, which examines how the chemical structure of the virus affects its biological activity, can also provide clues, although validation often takes a long time.
The first analyzes of the structure-to-activity relationship focused on the relationship between three mutations and Delta’s behavior. In particular, a pre-publication study, which has not yet been peer-reviewed, suggests that three mutations in the SARS-CoV-2 spike protein may make the variant more transmissible by facilitating the binding of this protein to the receptor. human cells (known as the ACE2 receptor).
If we go back to the analogy from the book, it means that three of the pieces cut out in the Delta version of the book are different from the original. Each of these three pieces can make it easier for the virus to infect human cells.
What do we know about the epidemiology of the Delta variant and its hot spots?
Everything suggests that Delta played an important role in the wave of Covid-19 cases observed in India in 2021. Since then, this variant has spread around the world. As of June 14, the Delta variant has been detected in 74 countries, accounted for over 90% of new cases in the UK and at least 6% of total cases in the US, with estimates going up to 10% .
Much of what we know about the Delta variant comes from Public Health England. It was first detected in the UK towards the end of March 2021, and linked to travel. As of June 9, the number of confirmed or probable cases stood at 42,323, with a well-distributed distribution across the country.
In Canada, Delta was first detected in early April in British Columbia.
Although Alpha is still the most dominant in the country, Delta’s growth has accelerated in many provinces. The number of confirmed cases jumped 66% in Canada last week, according to the Public Health Agency of Canada (PHAC). It is now present in all provinces and at least one of the territories.
Data from Alberta shows the number of cases is doubling every six to twelve days. Ontario has estimated that 40% of its new cases since June 14, 2021 are due to Delta.
Quebec is less affected: there are 35 cases of the Delta variant, especially in Montreal (21) and Montérégie (7), according to the latest data on the website of the National Institute of Public Health of Quebec.
It should be noted, however, that the prevalence of Delta is underestimated because an effective screening test has not yet been developed.