Interim results are in from a large trial of an experimental COVID-19 vaccine. Drug maker Pfizer, working with German company BioNTech, says its vaccine appears to be working really well — it was found to be more than 90 percent effective. Today on Short Wave, host Maddie Sofia talks to NPR science correspondent Joe Palca about what that efficacy number means, details of the study and what more information about the vaccine researchers are awaiting.Reach the show by emailing us at shortwave@npr.org.