CBS News
COVID-19 vaccine maker Moderna will make a third booster shot for its two-dose vaccine available to Americans by the fall, CEO Stéphane Bancel said this week. Moderna's vaccine is more than 90% effective against the coronavirus six months after the second shot, studies show. What remains unclear is how long immunity from the virus lasts. The same is true of Pfizer's two-dose COVID-19 vaccine.