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Illustration: Annelise Capossela/Axios

A new preprint study that raises concerns about the mRNA vaccines' effectiveness against Delta — particularly Pfizer's — has already grabbed the attention of top Biden administration officials.

What they're saying: The study found the Pfizer vaccine was only 42% effective against infection in July, when the Delta variant was dominant. "If that's not a wakeup call, I don't know what is," a senior Biden official told Axios.

Driving the news: The study, conducted by nference and the Mayo Clinic, compared the effectiveness of the Pfizer and Moderna vaccines in the Mayo Clinic Health System over time from January to July.

  • Overall, it found that the Moderna vaccine was 86% effective against infection over the study period, and Pfizer's was 76%. Moderna's vaccine was 92% effective against hospitalization and Pfizer's was 85%.
  • But the vaccines' effectiveness against infection dropped sharply in July, when the Delta variant's prevalence in Minnesota had risen to over 70%.
  • Moderna was 76% effective against infection, and Pfizer was only 42% effective.
  • The study found similar results in other states. For example, in Florida, the risk of infection in July for people fully vaccinated with Moderna was about 60% lower than for people fully vaccinated with Pfizer.

Why it matters: Although it has yet to be peer-reviewed, the study raises serious questions about both vaccines' long-term effectiveness, particularly Pfizer's.

  • It's unclear whether the results signify a reduction in effectiveness over time, a reduced effectiveness against Delta, or a combination of both.
  • “Based on the data that we have so far, it is a combination of both factors," said Venky Soundararajan, a lead author of the study. "The Moderna vaccine is likely — very likely — more effective than the Pfizer vaccine in areas where Delta is the dominant strain, and the Pfizer vaccine appears to have a lower durability of effectiveness.”
  • He added that his team is working on a follow-up study that will try to differentiate between the durability of the two vaccines and their effectiveness against Delta.

Yes, but: There has been no data so far that has found either vaccine's protection against severe disease and death is significantly less against Delta, and the study notes that there doesn't appear to be much of a difference in complications stemming from breakthrough infections based on which vaccine someone got.

  • And experts cautioned against rushing to conclusions.
  • “This is the kind of surprising finding that needs confirmation before we should accept its validity," said Cornell virologist John Moore.

Between the lines: The two shots both use mRNA, but there are significant differences between them.

  • For example, Moderna is given in a stronger dose than Pfizer, and there is a slightly different time interval between shots.
  • "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," Moore said.

In a statement, 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."

Editor's note: This story has been updated to include a statement from Pfizer.

Go deeper

Updated Nov 18, 2021 - Health

Florida governor signs bills limiting COVID vaccine mandates

Flordia Gov. Ron DeSantis. Photo: Paul Hennessy/SOPA Images/LightRocket via Getty Images

Florida Gov. Ron DeSantis signed into law Thursday four bills passed by Republicans that protect workers who refuse to get vaccinated against COVID-19.

Why it matters: With the bills signed, Florida becomes the first state with a law imposing possible fines on companies that require a COVID-19 vaccine as a condition of employment, CNN reports.

Fear and loneliness caused surge of early pandemic calls for help

Expand chart
Source: Brülhart, M., Klotzbücher, V., Lalive, R. et al. in Nature; Chart: Thomas Oide/Axios

Fear and loneliness replaced relationship and livelihood concerns during the pandemic, a team of scientists said after looking at millions of helpline calls in multiple countries before and after the COVID-19 pandemic started.

The big picture: Doctors and policymakers are trying to assess the impact of quarantines, school closures and other public health measures on our emotional and mental well-being. Using helpline data could become an important assessment tool, the researchers said.

Nov 18, 2021 - Health

Health groups urge businesses to voluntarily implement Biden's vaccine rule

Photo: Nick Oxford/Bloomberg via Getty Images

The American Medical Association (AMA) and more than 60 other health groups on Thursday urged companies with over 100 employees to voluntarily implement President Biden's vaccine-or-testing mandate, saying the requirements are "essential to protect workers."

Driving the news: The Department of Labor’s Occupational Safety and Health Administration (OSHA) issued the rule earlier this month, prompting immediate legal challenges. OSHA has suspended its enforcement of the rule pending further legal developments.