Box of vials of the 2023 Covid-19 vaccine. This vaccine protects against the SARS-CoV-2 virus subvariant XBB.1.5. It contains mRNA (messenger ribonucleic acid) strands that code for the spike protein found on the virus. When injected, the mRNA particles are taken up by the body's cells, instructing them to make copies of the spike protein, which stimulates an immune response, causing the body to produce antibodies against the spike protein. This means that the body is primed to attack the virus should they be encountered after vaccination, preventing disease.