Monday, May 10

SARS-CoV-2: contagiousness, frequency, resistance to the vaccine … what we know about the main variants

When they multiply, viruses can develop mutations, that is, errors leading to changes in the original genetic sequence, giving rise to variants. This is the case with SARS-CoV-2 like other viruses: it is an expected and common phenomenon.

Some errors have no consequences, others give it new adaptability. Some variants can become:

  • more contagious;
  • more virulent;
  • less sensitive to the immunity acquired by an infection or a vaccination: we speak of“Immune escape”.

Variants are classified into three categories by the World Health Organization (WHO) and monitored in international databases, including that of the Global Initiative on Sharing Avian Influenza Data (Gisaid):

  • variants of concern (or VOC for variant of concern) compared to the root virus. They are more virulent, more resistant to diagnostic tests, treatments or vaccines;
  • variants under surveillance (or VOI variant of interest), whose impact on public health has not yet been determined but which is found in several cases of contamination or at the origin of areas of contamination (clusters) ;
  • the variants under evaluation, whose consequences for public health are still undetermined.

According to Public health France, the worrisome variants currently circulating in France are the British, South African and Brazilian variants. The Indian variant is ” under surveillance “.

Queue in Saint-Denis (Seine-Saint-Denis) for the vaccination against Covid-19, April 26, 2021.
Read also Clear ideas on Covid-19: the variants
  • The British variant (B.1.1.7)

Also called “B.1.1.7”, it is reported in December 2020 by the United Kingdom, where it has become the main strain. Highly contagious, it is widespread in 139 countries and represents 83% of Covid-19 cases in France. “A virus capable of easily infecting humans will tend to multiply much faster. This is typically the case with the British variant ”, explains Vincent Maréchal, professor of virology at the University of the Sorbonne.

This increased transmissibility about + 43% to + 90% compared to the original virus is due to a mutation that affects the protein Spike, the main target of the immune response and through which the virus enters the cell. “This 501 mutation is associated, in the laboratory, with a greater affinity of the virus for its receptor on the surface of the cells it wants to infect”, explains Jean-Claude Manuguerra, head of the Biological Emergency Response Unit (CIBU) at the Institut Pasteur.

The British variant is also more virulent and results in more severe forms of the disease with a higher risk of hospitalization (from + 40% to + 64%) and a higher mortality (from + 30% to 70%).

On the other hand, it is not considered as an “escape variant”, it does not have the genetic modification responsible for the resistance which is also found on the Spike protein and bears the name of E484K.

In his weekly epidemiological report, WHO believes that the vaccines are globally effective against the British variant, with the exception of that of AstraZeneca which may not sufficiently block the transmission of the virus. A conclusion qualified by the WHO which specifies that the study was carried out on a small sample of patients and that other experimental data are necessary.

In France, the High Authority for Health (HAS) recommended the use of the four available vaccines, for which she believes the data “Suggest that they remain active against the English variant”.

Read the decryption: Nine questions about the new SARS-CoV-2 variant seen in the UK
  • South African variant (B.1.351)

The B.1.351 variant appeared at the end of 2020, first in South Africa and is now circulating in 87 countries, according to the WHO. Today he represents 5% of cases in France, 35% in Moselle and the majority in Mayotte and Reunion.

Just like the British variant, it has a mutation at position 501 which makes it more contagious (+ 50%) but also has an additional mutation, E484K, which also makes it more resistant to certain vaccines and could be the cause reinfections. According to the scientific council, this variant is the one that “Presents the most risk [d’échappement].

A scientific note of the US Centers for Disease Control and Prevention (CDC), states that, “In all the studies, the reductions [de l’efficacité des vaccins] the most important were observed for B.1.351 [sud-africain], followed by P.1 [brésilien].

The French scientific council explains in its February 12 note that messenger RNA vaccines (mRNA, such as Pfizer or Moderna) have a 30% reduction in efficacy on this variant. The sensitivity to the Janssen vaccine is also preserved: of the order of 50% with an 85% protection against severe forms. The AstraZeneca vaccine “Is only 60% -65% effective”, he recalls, believing that“An efficiency of 30% [sur ce variant] wouldn’t be amazing ”.

The P1 variant was detected on January 2 in a Japanese tourist returning from Brazil. It has spread to over 54 countries and is responsible for 5% of cases of Covid-19. In Guyana, it has become the majority.

The Brazilian variant is more contagious (mutation in 501) and more resistant vaccines (E484K mutation) and could cause re-infection. A significant proportion of patients with a severe form of Covid-19 are under the age of 50 in Brazil, says the scientific council in its opinion delivered on April 16.

However, its resistance to vaccines remains lower than that of the South African variant. The scientific council reports that the effectiveness of vaccines on the Brazilian variant is “Preserved but reduced”. It remains only partially inhibited by antibodies from individuals infected with the original virus.

Given the strong presence of the Brazilian and South African variants in overseas territories, the HAS recommended “The continuation of the strategy already in place with the exclusive use of messenger RNA vaccines. “

The B.1.617 variant was first detected in India in October 2020 and, according to the WHO, it is now present in 17 countries. The organization adds that most of the detected cases come from India, the United Kingdom, the United States and Singapore. On April 29, three cases of contamination with the Indian variant were identified in mainland France.

It has fifteen mutations, two of which are common with other variants. It is classified as a variant under surveillance but approximates the variants of known concern, even though it does not have the 501 mutation. scientific Council precise : “The E484Q mutation is close to but different from the E484K mutation which facilitates partial escape from vaccines. We can therefore expect a conserved but reduced vaccine efficacy. “ However, no prediction about its drivetrain or exhaust potential can yet be made.

“The urgency remains to vaccinate, recalls Jean-Claude Manuguerra of the Institut Pasteur. It’s a race against time, there must be as many people as possible vaccinated before variants can take hold or be generated. “ And for good reason, the more a virus circulates, the more it multiplies, which increases the probability of obtaining beneficial mutations for the virus, making the battle against the latter more complex.

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