Americans have received more than 120 million COVID-19 vaccine doses. Another 2.4 million shots are administered each day. Within the next few months, every adult in the U.S. who wants to be vaccinated will be. But there's a big unanswered question that affects anyone who receives a COVID-19 vaccine: How long will the vaccines provide protection against novel coronavirus infection? This isn't like the old TV game show The $64,000 Question, though. How long COVID-19 vaccines last is a multibillion-dollar question. Billions of dollars on the line Pfizer (NYSE: PFE) and BioNTech (NASDAQ: BNTX) were the first to win U.S....