Studies in favor of an increased dangerousness of the Delta variant are increasing. The latest is published on August 27 in the journal The Lancet Infectious Diseases. According to this British work, the hospitalization rate of people infected with the Delta variant would be doubled, compared to an infection with the Alpha variant. It should be noted that 98% of patients who tested positive in this study were not vaccinated.
The Delta variant, remember, is a mutated form of Sars-CoV-2, first detected in India in October 2020. It is much more contagious than its predecessor, the Alpha variant, which appeared in the United Kingdom in September. 2020 (compared to him, it is transmitted with an increased speed of 50%). The latter was already much more contagious than the historical strains of Sars-CoV-2, which appeared in China.
As contagious as chickenpox, the Delta variant has become the dominant form of the virus responsible for the Covid-19 pandemic around the world. At least 104 countries are facing it, according to the WHO. In France, this variant represented 98.1% of Sars-CoV-2 circulating on August 3, reported Public Health France in its bulletin of August 26. ” It is a variant that infects faster than its shadow », Observes Mahmoud Zureik, professor of epidemiology and public health at the University of Versailles – Saint Quentin-en-Yvelines.
A panel of more than 40,000 people
While there is no doubt about the increased contagiousness of the Delta variant, its degree of virulence – its harmfulness – is still debated. To answer this question, teams from the University of Cambridge analyzed data from 43,338 people who tested positive for Covid-19, in the United Kingdom, between March 29 and May 23, 2021. Vaccination status, age and others demographic factors and hospital admissions were scrutinized from their analysis. There were 51.1% women and 48.9% men; 30% were under 20 years old; 54.6% were between 20 and 50 years old and only 6.2% over 60 years old.
The authors identified 34,656 cases of the Alpha variant (80% of the patients), the majority in the United Kingdom at the start of the study, and 8,682 cases of the Delta variant (20% of the patients). But the latter’s proportion steadily increased during the follow-up period, reaching 65% in the last week.
The hospitalization rate gives a good idea of the virulence of the coronavirus: it is the severity of the disease that conditions admission to hospital. A total of 2.2% of people infected with the Alpha variant had to be hospitalized (764 people, out of a total of 34,656) within two weeks of their positive test, compared with 2.3% of people infected with the Delta variant (196 people, out of a total of 8,682). But the two groups were not strictly comparable (those infected with the Delta variant were younger, lived in poorer neighborhoods and more often belonged to an Indian ethnicity). To compare them, the authors had to do a sophisticated statistical analysis (called “stratified Cox regression”) “ necessary and well conducted », Greets Mircea Sofonea, lecturer in epidemiology at the University of Montpellier. Result: the Delta variant multiplies by 2.26 the risk of hospitalization, compared to its cousin Alpha.
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