Evidence indicating the emergence COVID-19 mutants has prompted concerns that available vaccines may not be able to offer protection against these new strains. However, a study using sera from patients given BNT162b2 suggests that the vaccine may still be effective.
There is nothing unusual about the ability of a virus to mutate although given the current pandemic, concerns have been expressed that the available vaccines may not offer enough protection against emerging strains. At the present time, there have been two notable COVID-19 strains: one first identified in the UK and which appears to be at least 70% more transmissible and the second, first identified in South Africa. There have been concerns expressed about this latter mutant because it appears to have mutations in the S glycoproteins, which are key targets of the virus neutralising antibodies generated in response to vaccination. It has been discovered that both the UK and South African variants share spike N501Y substitutions which are located in the viral receptor binding site for cell entry, allowing it to bind more effectively with the angiotensin converting enzyme 2.
In a small-scale study, researchers from the Department of Biochemistry and Molecular Biology, University of Texas, US, have tested antibodies generated by 20 patients given the BNT162b2 (i.e., the Pfizer vaccine) against a laboratory-developed isogenic COVID-19 variant that contained mutations in the N501 and Y501 regions and which is similar to the South African variant. Sera were drawn 2 or 4 weeks after immunisation with two doses of the vaccine, spaced three weeks apart. The team used the plaque reduction neutralisation test to quantify the tire of neutralising antibody generated against COVID-19. This test is considered to be the best and most widely used approach to measuring virus-neutralising and protective antibodies generated in response to a virus.
The results showed that there were equivalent neutralising titres generated in response to both the Y501 or N501 spike mutations which means that the vaccine is most likely to be effective. The authors noted a limitation of their findings was that the Y501 mutant does not contain the full set of mutations found in either the UK or South African variant. They concluded by calling for continuous monitoring of the virus which could necessitate a change in the vaccine strain.
Xie X et al. Neutralisation of N501Y mutant SARS-CoV-2 by BNT162b2 vaccine-elicited sera. BioRxiv 2021 doi.org/10.1101/2021.01.07.425740