NEW: @UKHSA study finds Pfizer booster is extremely effective against symptomatic infection, both compared to the unvaccinated and to those with 2 doses ft.com/content/8330da…
Whether first 2 doses were AZ or Pfizer, a Pfizer booster sends vaccine efficacy up to 93-94% 💪
Study was on people aged 50+, comparing those boosted ~5+ months after dose 2, to those @ 5+ months unboosted.
AZ efficacy was 61% after dose 2, waning to 44% @ 5 months.
Pfizer was 82% after dose 2, waning to 63% @ 5 months.
2 wks after Pfizer booster, both groups -> 93-94%!
Best way to think about booster impact is not to look at going from 44 to 93 with AZ, i.e roughly doubling, but invert the numbers and go from (100-44) to (100-93), i.e from relative risk vs unvaxxed of 56% to just 7%
That’s an 87% increase in protection *relative to two doses!*
More importantly, level of protection after a booster is *much higher* than it was even at peak level just after second dose.
For AZ, relative risk just after dose 2 was 39%, now it’s 7% — an 82% reduction.
For Pfizer, RR just after d2 was 18%, now it’s 6% — a 67% reduction.
In other words, a booster isn’t just topping us back up to where we were after we got our second dose (and remember how invincible that felt?), it’s taking us to higher levels of protection than we’ve ever seen.
Of course, big question is whether we’ll look back on this as first in a regular series of boosters, or the 3rd dose of a three-dose vaccine.
The higher levels of protection hint at this being a new dose rather than just a recurring top-up, but more time and research are needed.
One more note: the new study (and all numbers I’ve quoted) are specific to symptomatic infection with the Delta variant.
And finally, a link to the study itself: khub.net/documents/1359…
Oh, and even though this study only looked at efficacy against infection, not hospitalisation or death, we would strongly expect the same pattern to emerge there, even if only as a function of infection risk falling (and thus fewer people being susceptible to severe disease).
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