Most pandemic viruses jump to humans without prior adaptation, UC San Diego study finds
Mar 10th 2026
A UC San Diego study in Cell reports that most zoonotic viruses do not show special adaptations before infecting humans, while lab passage leaves clear genetic signatures, with 1977 H1N1 as a notable exception.
- A genome-wide phylogenetic analysis published in Cell found no evidence of pre-spillover adaptive evolution for most zoonotic viruses.
- SARS-CoV-2 shows no genetic signal of selection consistent with laboratory adaptation or prolonged evolution in an intermediate host prior to emergence.
- The 1977 H1N1 strain is an outlier that displays genetic signatures consistent with laboratory passage.
- The team validated their method with known lab-passaged controls and measured changes in selection intensity across whole viral genomes.
- The results offer a genomic benchmark to help distinguish natural spillovers from scenarios involving lab handling and to guide surveillance priorities.