I read two differing opinions about corona,

one from CDC that says

get your second shot as close to the recommended 3-week or 4-week interval as possible

Other from BBC UK, that says

Covid vaccine: Eight-week gap seen as sweet spot for Pfizer jab antibodies

So my question is why so much variation ? Humans in USA and Humans in UK are not that much different biologically ?

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    Perhaps researching the origins of the recommendations you list above would help. Who exactly recommended the "recommended 3-week" interval in the US? What data was that recommendation based on? What data underlies the BBC story you linked? Is the "eight week gap" an actual guideline? If so, who made it and why?
    – Armand
    Sep 21, 2021 at 18:32
  • The author of the answer self-deleted it after getting downvotes for not referencing.
    – Bryan Krause
    Sep 21, 2021 at 23:00
  • Your question is perfectly fine and the vanished answer you saw was deleted by its author as @BryanKrause described. Hopefully, they'll find the time to return and write an answer with a supporting reference or two.
    – Carey Gregory
    Sep 23, 2021 at 4:52
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    @puzzled To start with, you are asking about apples and oranges, as I suggested in my comment above. CDC is a recommendation on what to do based on some scientific results. Your BBC story is about scientific results (different than the science the CDC used), not a "what to do" recommendation.
    – Armand
    Sep 25, 2021 at 21:42
  • @armand Respectfully I do not think that I am asking apple and orange type question. Though thanks for the attention on the question.
    – puzzled
    Sep 28, 2021 at 2:05

1 Answer 1


In hindsight, the UK guideline was probably a good idea largely because a longer gap seems to lead to much longer-lasting immunity. Dr Campbell MD has a YouTube video in which he provides evidence to support this claim of his that the longer gap is the reason that the UK had much less of a spike in cases recently than Israel did, and extrapolates to the US.


Initially, the reasoning behind the NHS not following the manufacturers' dosing gap instructions that had been followed in the Phase 2/3 trial which demonstrated efficacy (and the US chose this conservative option) the was that x people getting 1 dose would have more societal benefit than x/2 people getting 2 doses, because it was felt that the marginal benefit of a second dose was smaller than of the first. In other words, the basis for the decision was fundamentally political, but grounded in evidence of relative impact of each shot.

https://www.gov.uk/government/news/statement-from-the-uk-chief-medical-officers-on-the-prioritisation-of-first-doses-of-covid-19-vaccines states,

The 4 UK Chief Medical Officers agree with the Joint Committee on Vaccination and Immunisation (JCVI) that at this stage of the pandemic prioritising the first doses of vaccine for as many people as possible on the priority list will protect the greatest number of at risk people overall in the shortest possible time and will have the greatest impact on reducing mortality, severe disease and hospitalisations and in protecting the NHS and equivalent health services. Operationally this will mean that second doses of both vaccines will be administered towards the end of the recommended vaccine dosing schedule of 12 weeks. This will maximise the number of people getting vaccine and therefore receiving protection in the next 12 weeks.

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    You're missing the simple reason for the US CDC guideline: their guideline is based on how the phase 3 trials were run. They didn't have phase 3 trial data for other gaps. All the efficacy data was based on the 3-4 week interval, that data showed good efficacy, so that's what they recommended. Using any other interval could result in different efficacy, but at the time there wasn't enough data to know in which direction.
    – Bryan Krause
    Sep 30, 2021 at 15:17
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    @whos-notooldrx4covidismurder thanks for attention to my question
    – puzzled
    Oct 2, 2021 at 18:25
  • I had stated that the manufacturers' dosing gap instructions that had been followed in the Phase 2/3 trial demonstrated efficacy. How is it not then obvious that a different gap wouldn’t necessarily demonstrate the same efficacy? There was even enough data from other jabs to make an educated guess as to which direction it would go with a longer gap. Oct 2, 2021 at 19:13
  • @WHO'sNoToOldRx4CovidIsMurder I think Bryan's just pointing out that the OP was also asking about US CDC guidelines, while your answer was dealing with UK guidelines and practices.
    – Armand
    Oct 3, 2021 at 20:45
  • Reasons for the US CDC recommending a gap not in accordance with best practice evidence would be speculative, to my knowledge. I don’t have evidence of reasoning behind the present, stale recommendation (<6 weeks) from the CDC being what Krause Oct 3, 2021 at 21:07

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