The first COVID-19 vaccine to win emergency use authorization in the U.S. is highly effective for at least six months after the second dose. Developed jointly by Pfizer (NYSE: PFE) and BioNTech (NSDQ: BNTX), the BNT162b2 vaccine   The durability of COVID-19 vaccines had been something of an open question, although early clinical data suggested that Moderna’s…