Two strains of Covid-19. Sars-2CovD from China mutated to Sars-2CovG which spread to Europe and mutated. That strain spread to the US. A single amino acid changed from D (aspartate) to G (glycine) on the CoV-2 spike protein. Sars-2Cov G is more infectious and having had Sars-2Cov D may not provide immunity for Sars-2 Cov G. So it's not a reinfection it's a second infection. There's no evidence the second virus is any less deadly, it may be more infectious. Hopefully it doesn't mutate again and "reinfection" is isolated. If having Covid-19 doesn't provide immunity, a successful vaccine could be impossible much like rhinovirus the common cold, also a coronavirus. Let's hope that's not the case.