Real-world proof Pfizer and Moderna mRNA vaccines prevent SARS-CoV-2 infection Several randomized placebo-controlled Phase III trials have shown that messenger RNA (mRNA) vaccines for COVID-19 effectively prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the effectiveness of these vaccines in preventing asymptomatic and symptomatic COVID-19 infections is not well understood. A new Morbidity and Mortality Weekly Report published by the U.S. Centers for Disease Control and Prevention (CDC) states that mRNA COVID-19 vaccines are highly effective in preventing SARS-CoV-2 infection in the real world. The report is based on a CDC study where it routinely tested prospective cohorts of health care professionals, first responders, and essential and frontline workers for SARS-CoV-2 infections.