Pennsylvania, New Jersey and Delaware are all moving to partially reopen. But health experts say only a COVID-19 vaccine can get us back to life (mostly) as we knew it, so scientists and pharmaceutical companies around the world —including some right here in the Philly area — are racing to make one ASAP. Dr. Paul Offit, who directs the Vaccine Education center at the Children’s Hospital of Philadelphia, is on a national panel overseeing vaccines being developed by American companies. He explains why vaccines take years to develop safely and why he urges companies “crowing” about their latest developments to be more humble.