Non-Peer Reviewed Study Raises Questions About Pfizer Vaccine Effectiveness Against Delta Variant

As fear spreads about the coronavirus Delta variant, a new preprint study suggests that the Pfizer and Moderna vaccines may be less effective over time.

Between the months of January and July, the study conducted by nference and the Mayo Clinic compared the effectiveness of both the Pfizer and the Moderna vaccines over the course of time. Axios profiled the study’s findings:

Overall, it found that the Moderna vaccine was 86% effective against infection over the study period, and Pfizer’s was 76%. Moderna’s vaccine was 92% effective against hospitalization and Pfizer’s was 85%.

But the vaccines’ effectiveness against infection dropped sharply in July, when the Delta variant’s prevalence in Minnesota had risen to over 70%.

Moderna was 76% effective against infection, and Pfizer was only 42% effective.

The study found similar results in other states. For example, in Florida, the risk of infection in July for people fully vaccinated with Moderna was about 60% lower than for people fully vaccinated with Pfizer.

The study did not determine if the vaccines declined in effectiveness over time, or were simply less effective against the Delta variant. Either way, the study’s findings have since become a cause for concern in the Biden administration, many of whom believe it may be a “wakeup call” for the current challenge at hand. However, it should be noted that the study has yet to be peer-reviewed and cannot be taken as gospel.

Venky Soundararajan, a lead author of the study, said that the data certainly raise important questions about the differences between the Moderna and Pfizer vaccines.

“Based on the data that we have so far, it is a combination of both factors,” Soundararajan said. “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.”

Cornell virologist John Moore said that even though the study had some surprising takeaways, more data would be needed before medical professionals “accept its validity.”

The presence of the Delta variant has played a major factor in the Biden administration’s call for mass vaccinations, even among youth.

“Here’s the deal: The Delta variant is more contagious, it’s deadlier, and it’s spreading quickly around the world – leaving young, unvaccinated people more vulnerable than ever. Please, get vaccinated if you haven’t already. Let’s head off this strain before it’s too late,” President Joe Biden tweeted in late June:

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