The grand plan Jim is to place as many people out of harm's way as possible, while Covid 19 infects others until it runs out of viable hosts and starts to dissipate. The problem is that in our densely populated cities, it will have plenty of new hosts, now matter how careful the lockdown ... People can't live in laboratory conditions after all.
A vaccine presents risks in itself, as the virus has no need to evolve while it's reproduction is unhindered.
A vaccine could well see a future outbreak of Covid 19 on steroids, as it adaps to counter the vaccine. Perhaps presenting the world with a considerably more lethal outbreak.