evidence: What they're saying: The study found the Pfizer vaccine was only 42% effective against infection in July, when the Delta variant was dominant. "If that's not a wakeup call, I don't know what is," a senior Biden official told Axios. Driving the news: The study, conducted by nference and the Mayo Clinic, compared the effectiveness of the Pfizer and Moderna vaccines in the Mayo Clinic Health System over time from January to July. [...] Moderna was 76% effective against infection, and Pfizer was only 42% effective.