Plus there is the question of what do we do with a variant that the vaccines provide less protection against. If there are thousands and thousands of cases in the community already it’s way too late contain except via a lockdown.
There's no evidence that any of the vaccines provide less protection from being ill or death though, is there.
The basics are there and people's immune systems are mostly enough. With the added bonus of the vaccine, the majority are absolutely fine.
The risk would be a variant that is totally immune developing but wouldn't that go against the history of every single virus ever? It is very unlikely that a variant of such potency will develop, but to insure that vulnerable/older groups have extra protection, the answer will be boosters which they're working on and it looks like they'll be out with the flu jab in the autumn? But in the meantime you just have to keep using what you have, seeing what happens as you reopen.
Risks have to be taken. The vaccines are offering massive mitigation against those risks - as we're seeing right now.