Frederic Bushman of the Perelman School of Medicine spoke about a recent study that found that more than one-third of Philadelphia COVID-19 infections were caused by variants of the virus. “The fear is that the virus is evolving to infect people more efficiently,” he said.
https://whyy.org/articles/pa-coronavirus-update-north-philly-to-get-vaccination-site-study-finds-variants-spread-in-city/ WHYY (Philadelphia)