Moderna will make a third dose of its coronavirus vaccine available in the fall as a booster shot to bolster immunity, according to CEO Stéphane Bancel. Though the double-shot preventative was more than 90 percent effective at preventing infection in clinical trials, the lifespan of the immunity remains unclear. Pfizer’s CEO made a similar remark Thursday, saying that a third dose of the company’s coronavirus vaccine would likely be necessary within 12 months of receiving the first two to maintain protection. According to the CDC, nearly a quarter of the U.S. population has been fully inoculated against COVID-19, whether with the Pfizer, Moderna, or now-paused Johnson & Johnson jab.