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US study: Moderna vaccine far better than Pfizer at preventing Delta infection

Mayo Clinic research finds both inoculations have dropped in efficacy, but Pfizer’s decline has been much steeper; both remain highly effective against severe illness

In this Wednesday, May 19, 2021 file photo, a licensed practical nurse draws a Moderna COVID-19 vaccine into a syringe at a mass vaccination clinic at Gillette Stadium in Foxborough, Mass. (AP Photo/Steven Senne)
In this Wednesday, May 19, 2021 file photo, a licensed practical nurse draws a Moderna COVID-19 vaccine into a syringe at a mass vaccination clinic at Gillette Stadium in Foxborough, Mass. (AP Photo/Steven Senne)

Moderna’s coronavirus vaccine is considerably more effective at repelling the Delta variant of the virus than Pfizer-BioNTech’s inoculation, according to research conducted in several US states by the Mayo Clinic.

The study uploaded to medRxiv ahead of peer review this week found that while both vaccines were highly effective in preventing infection in January, before the introduction of Delta — hovering at around 90 percent — by July the effectiveness of both shots had dropped.

However, one was still far more effective than the other — while Moderna was down to 76 percent, Pfizer was down to 42%. The study was conducted among over 50,000 patients.

It is not currently known whether the drop in effectiveness is a result of Delta’s ability to bypass the vaccine, an erosion in protection offered over time, or a combination of both factors.

Israel, which has vaccinated its population almost exclusively with the Pfizer shot, is currently administering third doses to adults over 60 in the hope of raising protection. According to one top expert Tuesday, this effort may be bearing fruit.

The Mayo Clinic study found that across multiple states, those inoculated with Pfizer were twice as likely to experience a breakthrough infection despite being vaccinated, as compared to Moderna.

An Israel woman receives a third Pfizer-BioNTech COVID-19 vaccine in the central city of Ramat Hasharon, July 30, 2021. (AP Photo/Sebastian Scheiner)

“In Florida, which is currently experiencing its largest COVID-19 surge to date, the risk of infection in July after full vaccination with mRNA-1273 (the Moderna shot) was about 60% lower than after full vaccination with BNT162b2 (Pfizer),” the researchers said.

Still, both vaccines appeared to remain highly effective (over 90%) at preventing severe illness.

The researchers concluded that “our observational study highlights that while both mRNA COVID-19 vaccines strongly protect against infection and severe disease, further evaluation of mechanisms underlying differences in their effectiveness such as dosing regimens and vaccine composition are warranted.”

Israel has predominantly relied on Pfizer’s vaccine to inoculate its population, but has also purchased millions of doses of Moderna’s version.

Both companies are currently developing booster shots that will target newer variants such as Delta, but these will take many more months to reach the market.

The COVID-19 vaccine is Moderna’s only commercially approved product. It is also developing several vaccines that aim to guard against the flu, Zika and HIV among other viruses. Those are all in early stages of clinical testing, according to its website.

The company, which was formed to commercialize mRNA vaccine technology, said it had nearly doubled in size over the past year, from 930 employees to around 1,800. It reported $4.35 billion in total revenue, thanks to the vaccine and some grants.

The Associated Press contributed to this report.

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