The Washington Post, if the assertions of Covid-19 reinfection are proved it could complicate efforts to make a long-lasting vaccine, or to achieve herd immunity where most of the population has become immune to the virus."There is still not enough evidence or sufficient time since the virus first struck to draw firm conclusions about how people develop immunity to covid-19, how long it might last — or what might make it less robust in some individuals than in others," the report said.Doctors emphasize there is no evidence of widespread vulnerability to reinfection and that it is difficult to know what to make of these cases in the absence of detailed lab work, or medical studies documenting reinfections, the report said.Among the 20.