Give a inferred Alpha, Delta or Omicron status based on time alone.
Source:R/augment-avoncap.R
derive_genomic_variant.Rd
This relies on date period during which we are very confidence that the only variants circulating are of a given type. These are quite conservative estimates based on the frequency of sequenced cases in the bristol area (according to the Sanger centre and to cases identified in the hospital testing)