New study finds Pfizer vaccine may be less effective against Delta variant

The study found that the Pfizer vaccine was only 42% effective against the Delta variant
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Doses of the Pfizer Covid-19 vaccine
Doses of the Pfizer Covid-19 vaccine
(JACK GUEZ/AFP via Getty Images)

A new study is raising concerns about the efficacy of mRNA vaccines against the Delta variant of the coronavirus. 

The recently published paper found that the Pfizer vaccine was only 42% effective against the Delta variant, and the news is rattling Biden administration staff and policy makers. 

"If that's not a wakeup call, I don't know what is," one White House official told Axios. 

The study, which was conducted by nference and the Mayo Clinic, found that over the course of seven months, the Moderna vaccine was 86% effective against infection, and the Pfizer vaccine was 76% effective. Moderna proved to be 92% effective against hospitalization due to infection, and Pfizer was 85% effective in the same category. 

However, the efficacy of both vaccines dropped dramatically in July, when the Delta variant became the dominant strain of the illness. Pfizer, in particular, dropped to 42% effective against infection, while Moderna fell to 76%. The results stemmed primarily from a group of individuals tested in Minnesota, but researchers found similar results in other states. 

In Florida, for instance, the study found that risk of infection in July for those with the Moderna vaccine was close to 60% lower than for those vaccinated with Pfizer.

The study has yet to be peer-reviewed, but raises serious questions about the continued efficacy of both vaccines – especially Pfizer – as the virus continues to spread and mutate. 

In a stated response to the study, Pfizer and BioNTech said they "expect to be able to develop and produce a tailor-made vaccine against that variant in approximately 100 days after a decision to do so, subject to regulatory approval."