The risk of suffering a breakthrough COVID-19 infection with the delta variant after being fully vaccinated with the Moderna vaccine may be much lower than the risk for those who received the Pfizer vaccine, according to a new Mayo Clinic study that is awaiting a full review.
The study found that in July in Florida, where COVID cases are at an all-time high and the delta variant is prevalent, the risk of a breakthrough case was 60% lower for Moderna recipients as compared to Pfizer recipients.
Similarly, in Minnesota last month, the authors found that the Moderna vaccine (also known as mRNA-1273) was 76% effective at preventing infection, but the Pfizer vaccine (known as BNT162b2) was 42% effective.
"Comparing rates of infection between matched individuals fully vaccinated with mRNA-1273 versus BNT162b2 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 authors wrote in their abstract.
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To be sure, the authors found that both vaccines "strongly protect" against severe disease; the difference appears to be more about whether people get infected at all in the first place. The CDC has said the risk of infection is 8x higher in the unvaccinated than the vaccinated, and the risk of hospitalization or death is 25x higher.
The so-called pre-print study, which has not gone through a peer review or been published in an academic journal, was first released on Sunday, though gained more notice on Wednesday when Axios reported that the Biden administration is taking the data as a "wakeup call."
Pfizer told Axios that it and partner 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."
The company, in a subsequent statement, affirmed the effectiveness of its vaccines and said it was committed to developing boosters as well.
"Pfizer and BioNTech have put into place a robust booster research program to ensure that our vaccine continues to offer the highest degree of protection possible. Initial data of a third dose of the current vaccine demonstrates that a booster dose given at least 6 months after the second dose elicits high neutralization titers against the wild type, Beta, and Delta variants," Pfizer said in a statement/
Just last week, Moderna warned that breakthrough infections were on the rise, and said those who received its vaccine would likely need a booster shot before winter. And late last month, Pfizer also said a booster already in testing would be effective against the delta variant.
Data out of New Jersey, where delta now accounts for 90% of all positive COVID samples tested, earlier this week underscores the key points: Breakthrough infections still account for a very small share of new COVID hospitalizations, but that share is rising significantly in recent weeks.
More on the Delta Variant
Fully vaccinated New Jerseyans accounted for 18.5% of all new COVID cases in the period July 20-26, Gov. Phil Murphy said. More importantly: Those cases accounted for 3% of all new hospitalizations.
Murphy pointed to the data Monday as evidence that vaccines work, but for many, the fact that even 3% of hospitalized COVID patients were already vaccinated is a worry -- and so is the direction in which the breakthrough cases are trending.
That 3% representation of immunized people hospitalized with the virus in the period July 20 through July 26 is up substantially from the .004% representation in the period up to July 26.
Pfizer accounts for 30% of the more than 10.6 million vaccine doses administered in New Jersey to date, while Moderna accounts for about 21%, state data shows.
