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Mothership.sg ran this headline:

Moderna's Covid-19 shot 93% effective, 6 months after 2nd dose However, Pfizer reported that their shot efficacy would reduce to around 84 per cent over the same time period. [...]

Reuters reported that Moderna data compares favorably to that released by Pfizer and BioNTech last week in which they said their vaccine's efficacy waned around 6% every two months, declining to around 84% six months after the second shot.

Predictably though, the data comes from different studies. Is this a fair comparison (given that efficacy depends on the likelihood of infection etc., so may vary with the sample)?

(N.B.: off the top of my head it's not entirely implausible given that Moderna's vaccine delivers about 3 times as much mRNA per dose, but then there are numerous other factors to consider.)

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    Without a head-to-head comparison in the same patient groups with the same virus variants, we can't really know.
    – Armand
    Aug 10 at 16:17
  • FWTW, hot off the press "Moderna vaccine may be superior to Pfizer against Delta variant, study finds" nypost.com/2021/08/10/… At least this one appears to be a study in the same sample...
    – Fizz
    Aug 10 at 17:07
  • Since we like to see the actual science here, the link to the preprint is: medrxiv.org/content/10.1101/2021.08.06.21261707v1.full.pdf It's unclear whether vaccine efficiency is waning or if Pfizer doesn't do as well against delta and the increased fraction of delta accounts for the increase in breakthrough infections. Either way, it does seem from this that the Moderna vaccine is looking better than Pfizer.
    – Armand
    Aug 10 at 21:21

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