In October 2021, the companies announced positive topline results from the trial showing that a booster dose administered to individuals who previously received the Pfizer-BioNTech primary two-dose series demonstrated a relative vaccine efficacy of 95% when compared to those who did not receive a booster. Thus far, these are the first and only efficacy data disclosed from any randomized, controlled COVID-19 vaccine booster trial. The adverse event profile was generally consistent with other clinical safety data for the vaccine, with no new safety concerns identified.