evidence: As with most other COVID-19 vaccine designs, the Pfizer/BioNTech mRNA vaccine works by triggering an immune response against the spike protein of the SARS-CoV-2 virus, which sits on the surface of the virus and is what the virus uses to enter cells. [...] A CDC study found that during the omicron wave, adults who had received two doses of the Pfizer/BioNTech or Moderna vaccines had a 79% lower risk of dying or needing a ventilator if hospitalized with COVID-19, compared with unvaccinated adults. Those who had received a booster vaccine dose as well had a 94% lower risk. [...] The link between the Pfizer/BioNTech and Moderna vaccines and rare cases of heart inflammation has been confirmed in subsequent work. A 2024 report from the National Academies of Sciences, Engineering, and Medicine "found convincing evidence that established a causal relationship with myocarditis" for both vaccines. The report, which looked at potential vaccine harms that were the subject of compensation claims, was not able to establish a causal relationship between the two vaccines and any other purported harms — in some cases favoring rejection of a causal relationship and in others finding insufficient data to draw a conclusion.