Several effective and safe vaccines against SARS-CoV-2 are now on the market. They were developed in record time, and are based specifically on inhibiting the virus’ spike (S) surface protein. The S protein, and more particularly the RBD region, binds to the ACE2 region to enable entry of the viral particle into the cell. This trimeric protein (an assembly of 3 S proteins) is the principal target of neutralizing antibodies.
The Pfizer-BioNTech vaccine is one of these current vaccines and is based on mRNA technology (See News-COVID-19.info letter November 23-29 2020). The mRNA, coated in lipid fat, provides instructions to the body to manufacture the entirety or a part of the virus’ S protein. This S protein will then trigger an immune response against the viral protein.
How was the effectiveness of these 2 vaccines determined? Pfizer and BioNTech, in collaboration with institutional laboratories, have just published the first results obtained during their vaccine development but before the onset of clinical trials. Two versions of the vaccine were compared: the BNT162b1, which encodes a trimerized RBD domain, and the BNT162b2, which encodes the full-length S protein, locked in its pre-fusion conformation (See News-COVID-19.info letter January 18-24 2021). These 2 versions were tested firstly on mice, which were immunized with one or the other of the vaccines. An IgG antibody response was detected, as well as a strong response mediated by CD4 T lymphocytes (T cell helpers that activate other immune cells) and T CD8s (cytotoxics that destroy infected cells). This response was slightly more pronounced with the BNT162b2 version of the vaccine.