Azrael
circling Airstrip One
This is a good interview on the background.What makes coronaviruses like sars cov 2 so difficult to vaccinate for then?
In short, the challenges weren't all technical: there simply wasn't sufficient financial incentive to produce a vaccine for the coronaviruses already circulating in humans, given the symptoms. MERS is terrifying, but hasn't spread widely enough; and SARS was eliminated by old school public health methods.
Now we have of course have all the incentives we need to throw resources and expertise at the problem.