A Pfizer-funded large study of breakthrough infections in immunocompromised people following two doses of the Pfizer/BioNTech vaccine against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) concluded that the vaccine largely prevented such infections, but that immunocompromised people would be best served with a third dose of the vaccine for better protection.
Background
Over 43 million cases of coronavirus disease 2019 (COVID-19) cases arose in the USA by September 2021, of which almost 700,000 were fatal. Conversely, over 173 million people had received two doses of the Pfizer vaccine BNT162b2, which was reported to be 94% effective in preventing symptomatic illness, hospitalizations, and deaths related to COVID-19.
