A peer-reviewed study in Frontiers in Virology found that a 19-nucleotide RNA sequence in SARS-CoV-2's furin cleavage site — the feature that makes it uniquely infectious to humans — is identical to a sequence patented by Moderna in February 2016 for cancer research. Researchers calculated the probability of this occurring through natural evolution at 1-in-3-trillion. The furin cleavage site is what distinguishes SARS-CoV-2 from all other known SARS-like coronaviruses and is not found in any close relatives.