Weekly newsletter:
March 1-7 2021
Level difficulty:
Could the South African variant partially escape the effects of vaccination?
SARS-CoV-2 has infected 106 million people and killed 2.3 million. Several candidate vaccines have been developed by different companies (Novavax, Janssen, Moderna, Pfizer-BioNTech, Oxford-AstraZeneca), based on various technologies (RNA, adenovirus vectors…). All these vaccines have been developed using sequences of the surface spike (S) viral protein from the strain in Wuhan that was at the origin of the epidemic. Now the virus has mutated. We have to ask ourselves whether those vaccines already developed will remain effective.
In the course of recent weeks, a number of variants have appeared in different parts of the world. The 1st to be identified was the UK variant in October 2020. Others were then reported, notably the South African variant in October and the Brazilian variant in December. These new viral strains each have 9 to 12 mutations or deletions, mainly in the S protein, but with a common point: certain mutations are found in the RBD domain. The RBD (“Receptor Binding Domain”) is the region of the S protein that binds to the ACE2 cellular receptor, enabling the viral particle to enter the cell. This region is also the target for numerous neutralizing antibodies. Protection against infection, whether acquired naturally or through vaccination, depends on the blockage of this interaction between the RBD and the ACE2 cellular receptor.
The 3 variants have developed mutations within the RBD: N501Y in the UK variant, K417N, E484K and N501Y in the South African, and K417T, E484K and N501Y in the Brazilian. These mutations seem to give the 3 variants greater transmissibility, confirmed by the UK strain. This selective advantage has enabled them to quickly become majority strains in the areas where they have appeared.
South African variant
Researchers at the University of Oxford have evaluated the capacities of the South African variant to escape the immunity produced by previous natural infection by another strain or by vaccination (vaccines developed from sequences of the strain at the origin of the pandemic). To do this, they carried out neutralization tests on the South African variant using monoclonal antibodies, serum from already infected patients or serum from patients vaccinated with the Pfizer-BioNTech or the Oxford-Astra Zeneca vaccine.
They first of all carried out neutralization tests on the South African variant with the serum of patients already infected either with the Wuhan strain or the UK variant. It appeared that neutralization by the serum of patients infected with the Wuhan strain and, to a lesser extent, with the serum of patients infected with the UK variant, is less effective. A combination of 20 monoclonal antibodies targeting the S protein did not neutralize the South African variant overall. Very few of them are effective against this variant.
As regards neutralization by serum taken from vaccinated patients (Pfizer-BioNTech or Astra Zeneca), this was visibly less effective against the South African variant than against the original strain. Recent studies suggest that the Novavax vaccine will have only 60% effectiveness in South Africa, where the South African variant is present in 92% of cases, whereas its effectiveness against the original strain in more than 95%. And the Janssen vaccine could have only 57% effectiveness in South Africa (with 72% effectiveness against the Wuhan strain).
This can be represented as follows:
This study showed that the South African variant is more difficult to neutralize than the original Wuhan strain, whether using monoclonal antibodies, serum from infected patients, or serum from patients immunised against SARS-CoV-2 through vaccination.
