Thread by @john_actuary

The PHE paper presented to SAGE on vaccine efficacy waning is also published today. A quick run down of the paper, focussing on experience with Delta (orange dots).

For hospitalisation, the drop-off appears greater with AZ, though note the wide band of the latest point.

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Here we can see that there's a much more pronounced drop-off in the 65+ group. The AZ falls after 4 1/2months are of such an extent that I wonder what the rationale is for waiting 6 months for the booster dose?

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Note that whilst Pfizer looks much better in the 65+ analysis, once that is restricted to 80+, the drop off becomes more apparent with this vaccine too. Some of this may be because a proportion of this group had the 2nd dose after just 3 weeks.

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Turning to mortality, we can also see the waning effect, although it is less pronounced than for hospitalisation. Note that again it appears greater for AZ, although there is limited data at the longer durations.

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The greatest amount of data is for symptomatic disease, and we see that AZ efficacy falls to around 50% after 20 weeks, and around 70% for Pfizer at the same time period.

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A key point to note with efficacy is that the effect on numbers is determined by looking at the change in (100%-efficacy %).

So a fall, say, in efficacy against death from 95% to 90% doubles the numbers dying, (from 5% to 10%).

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Finally, I'd repeat that I'm puzzled why a six month gap is being mandated for original AZ recipients, given the evidence that efficacy against hospitalisation appears to be falling quickly before that point.

Report here:
7/7
assets.publishing.service.gov.uk/government/upl…