Biden Official Says New Study Is ‘Wake Up Call’ After Pfizer’s Efficacy Plummets to 42% as Delta Variant Takes Hold
A new preprint study showed mRNA vaccines’ effectiveness plummeted in July when Delta variant was dominant — with Moderna only 76% effective and Pfizer only 42% effective against infection.
A new preprint study that raises concerns about the effectiveness of mRNA COVID vaccines — particularly Pfizer’s — against the Delta variant has caught the attention of top Biden administration officials, Axios reported.The study found Pfizer-BioNTech’s vaccine was only 42% effective against infection in July, when the Delta variant was dominant. “If that’s not a wake up call, I don’t know what is,” a senior Biden official told Axios.
The study, which has yet to be peer-reviewed, compared the effectiveness of Moderna and Pfizer COVID vaccines in the Mayo Clinic Health System from January to July 2021, during which time either the Alpha or Delta variant were highly prevalent.
To determine vaccine effectiveness, researchers matched demographically and “clinically similar” unvaccinated, Moderna-vaccinated and Pfizer-vaccinated individuals by sex, race, ethnicity, state of residence, SARS-CoV-2 PCR testing history and date of vaccination, according to MedPage Today.
Clinical outcomes of interest included SARS-CoV-2 infection, COVID-associated hospitalization, ICU admission, mortality and breakthrough infection — defined as infection occurring at least 14 days after the second dose of mRNA vaccine.
Overall, researchers found Moderna’s vaccine was 86% effective against infection over the study period, and Pfizer’s was 76% effective. Moderna’s vaccine was 92% effective against hospitalization and Pfizer’s was 85% effective. There were no deaths in either cohort.
According to data from multiple states, breakthrough infections were less likely among the Moderna cohort versus the Pfizer cohort, and the rate of hospitalization was lower among those vaccinated with Moderna compared with Pfizer. The authors found that COVID-associated ICU admission rates were comparable.
But vaccine efficacy dropped sharply in July, when the Delta variant was more prevalent. Moderna was only 76% effective against infection and Pfizer was only 42% effective.
Researchers noted the Delta variant prevalence in Minnesota increased from 0.7% in May to over 70% in July, whereas the Alpha variant prevalence decreased from 85% to 13% over the same time period.
Comparing rates of infection between individuals fully vaccinated with Pfizer and Moderna across Mayo Clinic Health System sites in multiple states, including Minnesota, Wisconsin, Arizona, Florida and Iowa, Moderna conferred a two-fold risk reduction against breakthrough infection compared to Pfizer.
In Florida, the risk of infection in July after full vaccination with Moderna was about 60% lower than after full vaccination with Pfizer.
“We observed a pronounced reduction in the effectiveness of BNT162b2 [Pfizer] coinciding with the surging prevalence of the Delta variant in the United States, but this temporal association does not imply causality,” Venky Soundararajan and his co-authors wrote.
The authors concluded “further evaluation of mechanisms underlying differences in their effectiveness such as dosing regimens and vaccine composition are warranted.”
The two shots both use mRNA technology, but Moderna is given in a stronger dose than Pfizer, and there is a slightly different time interval between shots, Axios reported.
“There are a few differences between what are known to be similar vaccines … None of these variables is an obvious smoking gun, although the dosing amount seems the most likely to be a factor,” said Cornell virologist John Moore.
In a statement to Axios, Pfizer said it and BioNTech “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.
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