According to a large Canadian study, the Delta variant is 133% more deadly than the original covid 19. The emergence of different variants has thus considerably delayed the exit from the pandemic, even if vaccines remain effective in preventing severe forms.
The Delta variant, almost non-existent in January, now represents 99% of infections in France and 99.3% of sequences deposited in the Gisaid database at the international level for the period from August 29 to September 21, 2021, according to an analysis by Public Health France. Several studies have already attested to the greater contagiousness and virulence of the Delta variant (see diagram below). It is also more likely to escape the vaccine: the effectiveness rate of the Moderna and Pfizer vaccines drops to 66% with this variant, compared to more than 90% with the original virus.
A 133% increased risk of death
A large new study, conducted in Canada, confirms the extreme virulence of this variant. Conducted on 212,326 people between February and June 2021, the latter examined the risks of hospitalization, admission to the emergency room, and death related to the different variants then circulating (Alpha, Beta, Gamma, and Delta) compared to the original virus. As a result, the risk of hospitalization, admission to the emergency department, and death is increased by 108%, 235%, and 133% respectively with the Delta variant. In other words, where one in 100 people died from the original SARS-CoV-2, 2.33 people die when infected with the Delta variant.
Virulence is also higher with alpha, beta, and gamma variants, but to a lesser extent (52% for hospitalization risk, 89% for emergency department admission risk, and 51% for death risk). "Even adjusted for factors of age, sex, and comorbidities, the risk persists," the researchers insist. "The emergence of new variants of SARS-CoV-2 has slowed progress against the pandemic in three distinct ways," says David Fisman, co-author of the article published in the Canadian Medical Association Journal (CMAJ), namely by increasing the transmissibility and number of reproductions of the virus, increasing immune evasion, and increasing the virulence of infection.
The virus has become smarter and more dangerous
The good news is that if the vaccine remains very effective against severe forms. "Vaccines offer a substantial degree of protection against death (about 80 to 90%), even if they fail to prevent infection," the authors say. This helps reduce transmission of the virus, even though herd immunity is unattainable given the high reproductive rate. »
"We are facing a completely different epidemic than in 2020," Kirsten Patrick, CMAJ's editor-in-chief, confirms in an editorial accompanying the article. The virus has become smarter and more dangerous, which means we too need to be smarter. Governments must keep people safe by adopting policies that judiciously combine all the measures that have proven effective. It calls for the expansion of vaccination, the prohibition of anti-vaccination gatherings near schools and health facilities, the approval of safe vaccines for children, an effective international collaboration to ensure the administration of vaccines on a global scale, or the continuation of the work of identifying, monitoring and controlling the epidemic.
Unfortunately, the end of the pandemic is still not insight, and it is even likely that Covid will turn into an endemic. "We must expect a genetic diversification of the Delta variant in view of its intense circulation in the world in recent months," warns Public Health France. The relative share of some Delta sub-lineages (AY.4 in particular) compared to the initial B.1.617.2 lineage is increasing, although data are still lacking on the impact of these mutations. »
Delta variant is linked to increased risk of hospitalization
This was an unanswered question since its emergence: is the Delta variant more virulent than the Alpha variant? A study conducted by the English health authorities offers a beginning of an answer.
Since last August, 95% of new infections in France are due to the Delta variant. It supplanted the Alpha variant because of its high contagiousness, about 40 to 50% higher than that of its cousin. The symptoms it causes are milder and comparable to a big cold. Fever and anosmia typical of the Alpha variant are less common. Does this mean that the Delta variant is less virulent? According to scientists in the Covid cell of the English public health authority, no. Being infected with the Delta variant increases the risk of being hospitalized compared to the Alpha variant.
More risk of being hospitalized because of the Delta variant
The study was conducted on data collected between March 23 and May 29, 2021. At that time, the Delta variant was not yet the majority in England, but it was beginning to gain ground. Of the 43,338 Covid-19 positive patients included in the study, 8,682 were infected with the Delta variant and 34,656 with the Alpha variant. The infection and the nature of the variant responsible were confirmed by sequencing. The scientists calculated the risk factor of being admitted to the hospital within 14 days of diagnosis for a patient who tested positive for the Delta variant compared to the Alpha variant.
The adjusted hazard ratio (HR) of being admitted to the hospital within 14 days is 2.26. In other words, people infected with the Delta variant are about twice as likely to be admitted to the hospital as those infected with the Alpha variant. The majority of included patients (74%) were not vaccinated. The scientists performed the same calculation taking into account the vaccination status.
The effect of the vaccine?
The adjusted HR of being admitted to hospital for a person infected with the Delta variant compared to the Alpha variant is 2.32 for the first-vaccinated or unvaccinated, and 1.94 for those fully protected by the vaccine (21 days after the second dose). Nevertheless, the number of vaccinated considered here is too small to make a solid calculation. Also, this data will have to be confirmed by other studies.
These findings are in line with those of the Scottish public health authority, which conducted a similar but more modest study last June. The Delta variant appears to be linked to an increased risk of hospitalization compared to the Alpha variant. Through vaccination, this risk can be reduced. The epidemic peak we have just reached has been less severe for hospitals than last spring when vaccination was not yet open to all.
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