I was chatting to someone in they're final year of a medical degree, majoring in microbiology, and the comment came that there was a reason a vaccine has never been developed for SARS. The gist of the conversation was that vaccines don't work for cold and flu viruses because of the way they attack the body. The best they can hope for is a temporary immune response, which will last for 4 to 6 months in a healthy person. For a sick or compromised person they won't even get that. Hence why they're trying out the mrna approach, to circumnavigate this. We're basically a bunch of guinea pigs.