One Note Of Caution On The Big 'Real World' Assessment of Pfizer Vaccine Effectiveness.

TheActualDataAre
AlwaysTheDataVille

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Update: Friday Feb 26th...A direct assessment of asymptomatic subject strongly suggests one dose of the Pfizer mRNA vaccine strongly suppresses viral transmission...Details here.

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There is was a big peer-reviewed paper that came out in the New England Journal of Medicine yesterday on the effectiveness of the massive roll out of the Pfizer mRNA-based vaccine in Israel.

Helen Branswell, who is an excellent science journalist, has an solid first pass summary  STAT News. This is her lede:

Pfizer and BioNTech’s Covid-19 vaccine performed as well in the real world as it did in the clinical trial that led to its use, a large study conducted in Israel concluded.

The study, published Wednesday in the New England Journal of Medicine, is the largest to date assessing the effectiveness of the vaccine, comparing all illness, severe illness, and hospitalizations as well as deaths between 600,000 pairs of vaccinated and unvaccinated people...

All in all it's a great story in that vaccine effectiveness against symptomatic disease in the real world matches up well with what was found in the original phase III clinical trial.

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Now, there are some data in the paper on the reduction of viral infections that they were able to document. This led a few folks to take a leap re: effectiveness at preventing total viral infections (such a leap is something that I commented upon earlier on the basis of a different 'leaked' report). 

One of the authors of the New England Journal paper, Marc Lipsitch, who is an epidemiologist at Harvard, jumped in on a twitter thread to make the following very important cautionary point in that regard:

So, again, and this time according to an expert who was involved in yesterday's peer-reviewed, published study, the science is not yet settled regarding the ability of the Pfizer vaccine to prevent viral transmission that generates both symptomatic infections (easier to track) and asymptomatic infections (harder to track).

That does not mean that things do not look promising, as Dr. Lipsitch himself thinks that the overall protection against viral transmission by the mRNA vaccine is 80% or more. It's just that he does not believe we actually have the data to be sure about the number:

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Update...For more on the need for caution on claims of a specific rate of vaccine-mediated infection suppression (based on the data so far) see this very recent, solid piece by Megan Molteni in Wired.

Just to take off my science-guy hat for a moment and return to the usual discussion about what does or does not get wurlitzered in the public prints and/or social media...Dr. Lizsitch posted these comments late on Wednesday...I'm typing this late on Thursday and note how few retweets, etc. his comments, which are comments that actually matter, have received compared to, say, the usual suspects blathering on about essentially nothing....Just one of those things that makes you nod your head, eh?

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