Randomized Trial of COVID-19 Booster Vaccinations (Cobovax Study)

BNT162b2 is a nucleoside-modified mRNA encoding the trimerized SARS-CoV-2 spike glycoprotein. The vaccine is formulated in lipid nanoparticles that increase the efficiency of delivery of the mRNA into cells after intramuscular injection. BNT162b2 encodes the SARS- CoV-2 full-length spike, modified by two proline mutations to lock it in the prefusion conformation and more closely recreate the intact virus with which the elicited virus- neutralizing antibodies interact. mRNA vaccines use the pathogen's genetic code as the vaccine; hence they exploit the host cells to translate the code and generate the target spike protein. The protein then acts as an intracellular antigen to stimulate the immune response of the vaccinated individual. The mRNA is then degraded within days.

CoronaVac is a Vero cell-based, aluminium hydroxide-adjuvanted, β-propiolactone- inactivated vaccine based on the CZ02 strain. This strain of SARS-CoV-2 was isolated from the bronchoalveolar lavage of a hospitalized patient and is closely related to the 2019-nCoV- BetaCoV Wuhan/WIV04/2019 strain. Each 0.5 ml dose is composed of 3 μg of inactivated SARS-CoV-2 virus. The excipients are aluminium hydroxide, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium chloride, and water for injection.