A vaccine effectively teaches your immune system to fight a virus or bacteria. If our body can't learn on its own, then a vaccine is unlikely to be significantly more successful.
That said, there are definitely cases of someone getting it twice. Nothing is 100%, and hopefully these cases are outliers.
All that said, there has never been a successful vaccine to a coronavirus, although I believe they were close on SARS before it went away. Part of the reason for this is there is not a lot of money in a vaccine for the common cold.
There is another theory out there, that the virus is getting weaker on its own. Anyone that lived through March or April 2020 in the tri-state area will tell you that what we are going through now is nothing like it was back then around NYC, despite many more people being infected now. None of the stock arguments (better treatment, better social distancing) really address this fact. There were 423 deaths yesterday from a virus that has infected the entire country. On April 21, there were 2,748 from a virus that was in 5-6 states. Something is happening to the virus.
The virus weakening is logical from an evolutionary standpoint, and it is likely that one of the current strains of the common cold comes from a pandemic that hit in the early 19th century. Viruses do get weaker over time as the more virulent strains kill their host and don't replicate, while the weaker strains survive.
If the virus is weakening, then the right move for society is to maintain social distancing and "run out the clock" on it. We could be down to under 100 deaths a day by next summer if we just stay safe. If we open up too fast, we give the more virulent strains a chance to find new hosts.
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