We are nearly at a Universal Flu Vaccine- the next 5 years or so.
We have new technology.
Think of it like this. I ask you to sit on a highway bridge and throw a brick through the window of a black Lincoln Navigator with the license plate ‘Covid’. As a black Navigator approaches, you (the immune system) looks at it and sees the license plate and throw the brick.
Now the next Navigator to come along, you see it has the license plate ‘New Virus 2021’. You ignore that one and don’t throw your brick.
That’s how traditional vaccine works as when the mutation happens (license plate changes) you don’t recognise it as a threat.
Now imagine we made it impossible for you, the vaccine, to see the license plate. Now all you see is a black Navigator as you cannot see the thing that changes. So you have to throw a brick at every black Navigator.
That’s how the Universal Flu vaccine will basically work- the vaccine doesn’t trigger an immune response on the whole virus, just parts of it that don’t change.
It isn’t known if the Coronavirus vaccine will have to be repeated due to mutation. But maybe not. For example the Oxford Vaccine (the UK one that’s looking very promising) causes an immune response only against the crown spikes, not the rest of it.