It certainly confers immunity for a short period of time. How long that immunity lasts for is unknown, but it’s not unreasonable to start with an assumption of

It certainly confers immunity for a short period of time. How long that immunity lasts for is unknown, but it’s not unreasonable to start with an assumption of “at least a few months”. There’s also not strong evidence that there are two sufficiently different strains. Viruses experience small, mostly meaningless, mutations with great frequency. The research talking about S and L types are actually just an arbitrary categorization of many different mutations of the virus.