evidence: A new preprint study published in medRxiv suggests mRNA vaccines' efficacy against infection—particularly the Pfizer-BioNTech vaccine—has dropped significantly since the delta variant became widespread, although the vaccines' protection against hospitalization and death remain strong. [...] However, during the month of July, the vaccines' efficacy against infection appeared to decline in Minnesota, where the prevalence of the delta variant had increased from 0.7% in January to 70% in July. Specifically, the researchers found that during July, the Moderna vaccine appeared to have an estimated efficacy of 76% against infection, while the Pfizer-BioNTech vaccine had an estimated efficacy of 42% against infection. [...] However, Venky Soundararajan, a lead author on the study, said based on the data compiled so far, the vaccines' reduced efficacy likely stems from "a combination" of both reduced efficacy over time and reduced efficacy against the delta variant. "The Moderna vaccine is likely—very likely—more effective than the Pfizer vaccine in areas where delta is the dominant strain, and the Pfizer vaccine appears to have a lower durability of effectiveness," he said.