Box of vials of the 2023 Covid-19 vaccine. This vaccine protects against the original SARS-CoV-2 virus and two subvariants, BA.4 and BA.5. It contains mRNA (messenger ribonucleic acid) strands that code for the different spike proteins found on the viruses. When injected, the mRNA particles are taken up by the body's cells, instructing them to make copies of the spike proteins, which stimulates an immune response, causing the body to produce antibodies against the spike proteins. This means that the body is primed to attack the viruses should they be encountered after vaccination, preventing disease.