Moderna said its COVID-19 vaccine demonstrated 93 percent efficacy, with efficacy remaining durable through six months after the second dose's administration.
The announcement was based on a new analysis of its clinical trial, which began in July 2020 and enrolled 30,000 U.S. participants.
The new trial data was released just before an Aug. 5 earnings call. In the slides prepared for the call, Moderna said booster shots will most likely become necessary before winter to combat the rapid spread of the delta variant, which became widespread in the U.S. after the trial results were recorded.
"We believe that increased force of infection resulting from delta, non-pharmaceutical intervention fatigue, and seasonal effects (moving indoors) will lead to an increase of breakthrough infections in vaccinated individuals," the slides read. "While we see durable phase 3 efficacy through six months, we expect neutralizing titers will continue to wane and eventually impact vaccine efficacy. Given this intersection, we believe dose 3 booster will likely be necessary prior to the winter season."