Pfizer vaccine results leave questions about safety, longevity

Covid-19 results from Pfizer Inc. and BioNTech SE fueled optimism that the world will soon have a potential way out of the pandemic, yet experts cautioned that the shot still has many hurdles to clear. Questions about production, distribution and, most importantly, the performance and capability of the shot itself still need to be answered, even if the numbers look highly promising, according to vaccine specialists. The Pfizer trial started less than four months ago, and how long the vaccine will confer protection and how many will benefit are almost complete unknowns for now. “The key question still centers upon time,” said Michael Kinch, a drug development expert and associate vice...