Moderna 76%, Pfizer 42% effective against COVID-19 Delta variant: Mayo Clinic study

By Team Newsable | First Published Aug 12, 2021, 5:37 PM IST

A Mayo Clinic study peered at the effectiveness of mRNA vaccines between January and July.

The current Covid-19 vaccines in use might not be as effective against the Indian 'Delta' variant compared to the first strain of the virus, a new published study suggests.

Researchers from the Mayo Clinic in Minnesota, US, found that the Pfizer-BioNTech vaccine was only 42% effective against infection in July, while the Moderna vaccine was only 76% effective, the Daily Mail reported.

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"Comparing rates of infection between matched individuals fully vaccinated with mRNA-1273 (Moderna Covid vaccine) versus BNT162b2 (Pfizer Covid vaccine) across Mayo Clinic Health System sites in multiple states (Minnesota, Wisconsin, Arizona, Florida, and Iowa), mRNA-1273 conferred a two-fold risk reduction against breakthrough infection compared to BNT162b2," the researchers wrote within the study.

The study, which has not yet been peer reviewed, tracked the effectiveness of the mRNA vaccines between January and July.

Over the course of the study in Minnesota, Moderna's vaccine was found to be 86% effective against a Covid-19 infection while Pfizer's was 76% effective. Both were also highly effective against hospitalization (Moderna 91.6%, Pfizer 85%), ICU admission (Moderna 93.3%, Pfizer 87%), and death from Covid-19 (no cases found).

For the study, published on pre-printer server medRxiv.org - meaning it's not yet been reviewed - the team gathered data on quite 25,000 Minnesotans from January to July. The vaccines as claimed remained effective around 90% but began dipping in June and largely dropped in July because the variant took hold within the US.

The study doesn't say whether the drop by effectiveness is thanks to vaccines losing their potency over time, or because they are not as effective against Delta, or a mixture of both.

Pfizer told Axios during a statement that it expected "to be ready to develop and produce a tailor-made vaccine against" the Delta variant "in approximately 100 days after a choice to try to do so, subject to regulatory approval."

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