Safety concerns like Antibody-Dependent Enhancement (ADE) observed in past SARS vaccine work pose a significant challenge to rapid vaccine development.

“the questions would it be safe and effective and that's what's key so I think from an effectiveness standpoint I do think we can probably find something that will be effective even if temporarily meaning is not permanent long term protection but something might require boosters we don't really know that yet the whole t-cell b-cell combination of immunity with coronaviruses is still a question I'm more optimistic about that where I think is going to hold us up a lot is safety in the 2003 SARS vaccine work there was some real challenges that developed with the animals with something called antibody dependent enhanced with a de where if he made just a little bit of antibody that was bad because then when you got infected with the real thing you had this antibody dependent enhancement there was a shock like picture and it was a real challenge and that's exactly what happened the dengue vaccine in the Philippines that got pulled two years ago was that that vaccine had an a de component to it that nobody had appreciated”