The CDC classifies C-19 virus variants according to their "potential impact on critical SARS-CoV-2 countermeasures, including vaccines, therapeutics, and diagnostics." The worst category is "a variant of high consequence," which is defined by "clear evidence that prevention measures or medical countermeasures have significantly reduced effectiveness relative to previously circulating variants." As of March 16, 2021, the last sentence of the CDC's webpage on this topic states: "Currently there are no SARS-CoV-2 variants that rise to the level of high consequence." This accords with research published a year ago that found the C-19 virus "does not mutate rapidly for an RNA virus because, unusually for this category, it has a proof-reading function" in its genetics. A torrent of research has since confirmed that people who have recovered from C-19 are highly unlikely to be harmed by it, even if they are infected again.