At the Washington University School of Medicine, CDC Director, Rochelle Welensky, claimed her science was based on "too little caution and too much optimism" regarding the COVID-19 vaccines. She referenced a CNN article, from November 2020, when CNN reported that the Pfizer-BioNTech vaccine was 95% effective at preventing COVID-19.

"I can tell you where I was when the CNN feed came that it was 95% effective, the vaccine," Walensky said, responding to a question about what public health officials could have done better during the pandemic. "So many of us wanted to be helpful. So many of us wanted to say, ‘OK, this is our ticket out, right?’ ‘Now we’re done.’ So I think we had perhaps too little caution and too much optimism for some good things that came our way."