evidence: The Pfizer/BioNTech vaccine is the first COVID-19 vaccine approved by health agencies in the U.K. and the U.S. The clinical trials proved that the vaccine is safe and efficient at preventing COVID-19 infection. The main ingredient is a messenger RNA that encodes the SARS-CoV-2 spike protein, which is used to trigger an immune response. The other ingredients, including the lipids that allow the mRNA to enter human cells, are common in drug formulation.