Of course the trials are absolutely necessary, but I'm more worried about the manufacturing process. There will be a huge demand when the vaccine becomes available, and it will be tempting to rush production to meet demand.

Sometimes I think about the Cutter Incident:

In April 1955 more than 200 000 children in five Western and mid-Western USA states received a polio vaccine in which the process of inactivating the live virus proved to be defective. Within days there were reports of paralysis and within a month the first mass vaccination programme against polio had to be abandoned. Subsequent investigations revealed that the vaccine, manufactured by the California-based family firm of Cutter Laboratories, had caused 40 000 cases of polio, leaving 200 children with varying degrees of paralysis and killing 10.