What makes Pfizer's COVID-19 vaccine stand out from the others?

Pfizer announced big developments this week about their COVID-19 vaccine. Pfizer and BioNTech say early trial data show their vaccine is more than 90% effective. The news sent a shock through the stock market, and it gave a lot of people a glimmer of hope. So what’s next for Pfizer and this vaccine, and what makes it different from the dozens of other vaccines in the pipeline? Dr. Susan Ellenberg, professor of biostatistics and epidemiology at the University of Pennsylvania joins KYW Newsradio In Depth to break down what we know so far.