evidence: - It found Pfizer's effectiveness dropped to 42% in Minnesota in July, when Delta became dominant. [...] Pfizer's coronavirus vaccine might not be as good at preventing infection of the Delta variant as Moderna's, according to a new preprint from the Mayo Clinic and the analytics company Nference. [...] During that month in Minnesota, Pfizer's effectiveness against COVID-19 infection dropped to 42%, while Moderna's dropped less dramatically to 76%.