Moderna Vaccine May Shield More Against Breakthrough Infections Than Pfizer: Study

People fully vaccinated with the Moderna COVID-19 vaccine appear to have a lower risk for a "breakthrough" infection caused by the delta variant than those who received the Pfizer vaccine, a new, preliminary report suggests.

The researchers emphasized that both vaccines still "strongly protect" against severe illness, but the difference appears to be in the degree of protection they offer against infection. The infection risk was 60 percent lower among Moderna recipients than among Pfizer recipients, according to an analysis of July data from Florida, where the delta variant has driven COVID-19 cases to new highs.

The Mayo Clinic researchers also found that in Minnesota last month, the Moderna vaccine was 76 percent effective at preventing a breakthrough infection, while the Pfizer vaccine was only 42 percent effective.

"Comparing rates of infection between matched individuals fully vaccinated with mRNA-1273 [Moderna] versus BNT162b2 [Pfizer] across Mayo Clinic Health System sites in multiple states (Minnesota, Wisconsin, Arizona, Florida, and Iowa), mRNA-1273 conferred a twofold risk reduction against breakthrough infection compared to BNT162b2," the authors write.

The new data were published online Aug. 8 in medRxiv as a preprint study that is awaiting a full peer review, so the findings should be considered preliminary.