Biologically speaking SARS-CoV-2 is just one more coronavirus and isn't particularly special or unusual. We already know that prior infection with other coronaviruses such as HCoV-OC43 provides pretty good protection against symptomatic reinfection with the same coronavirus as long as the patient is otherwise healthy. If anyone claims that SARS-CoV-2 is somehow different then the burden of proof is on them; extraordinary claims require extraordinary evidence.

As for vaccines, we obviously can't have any data on long term effectiveness. But short term effectiveness against severe symptoms is pretty good, and periodic boosters are available to those who want them.