“Our analysis highlights that in the absence of vaccination, any delta outbreaks will impose a greater burden on healthcare than an alpha epidemic,” said Anne Presanis, one of the study’s lead authors and a senior statistician at Cambridge. “Getting fully vaccinated is crucial for reducing an individual’s risk of symptomatic infection with delta.”

“Our results suggest that the timing of exposure relative to primary-case symptoms is important for transmission, and this understanding provides further evidence that rapid testing and quarantine after someone is feeling sick is a critical step to control the epidemic,” Martinez said.