The right answer to Jack’s question can help use all that AstraZeneca

Jul 25, 2021

Jack1 from Bathurst phoned into Life Matters this week. He thought to help the Covid vaccine situation by bringing forward his second AstraZeneca jab. But no one could tell him what effect that would have on the efficacy of his jabs.

Jack’s second jab is due in mid-August. So he had the capacity to fast track it by four weeks. He called the local clinic and was told that he would lose 16% of immunity for each week the second jab was brought forward. Having “fallen out” with the person he was speaking to, he called again. Another clinician said he would lose 10% of immunity per week.

Jack’s question is a good one. It needs to be answered if those in a similar situation are to help by bringing forward their second AZ jab.

One of the experts on the Life Matters radio program gave some very precise figures about the efficacy of the two vaccines available to us in Australia – but did not directly answer Jack’s question. I thought there must surely be a table of such numbers somewhere, so I went searching online. I couldn’t find a consolidated tabulation but there are of course miles of research papers on individual aspects of the question.

So I started to compile my own. I have included in it the stats from the ABC interview with Associate Professor Margie Danchin. (I will be very happy to hear from someone about where I can find a decent, professional table of this sort. Surely?)

If Jack’s question is answered in such a way as to make it clear that there will be no, or very little, loss of efficacy by bringing forward the second jab, it will make a significant contribution to the acceleration of the effective use of AstraZeneca which so many people are now hoping for.

I’ve called it A current policy and information hotspot. All we need is reliable scientific evidence that there will be little loss of efficacy and a whole cohort of people who have already demonstrated their willingness to be vaccinated can provide an immediate boost to the nation’s well-being and prospects.

1 close to his real name.

efficacy of AstraZeneca and Pfizer against

and Delta variants

figures from a small
number of online sources

speedily compiled on
22 July 2021

Protective efficacy against
symptomatic Covid (Alpha)

Protective efficacy against
symptomatic Covid (Delta)

Protective efficacy against
hospitalisation due to Covid (Delta)

AstraZeneca, first dose



“barely any” in article in


Life Matters: 30%

“barely any” in article in


Life Matters: 71%

4 week gap – AstraZeneca 2nd dose



[If it was pro rata, 42%]


[If pro rata, 78%]

8 week gap – AstraZeneca 2nd dose




12 week gap – AstraZeneca 2nd dose


Life Matters: 81%

67% Life Matters

2 doses: 92% Life Matters.
But what gap?

Pfizer, first dose




“barely any”

Nature, Delphine Planas et al, 8 July2021

Pfizer, 3 week gap

(21 days rec.; best protection after 7
more days)


80% for ‘infection’

88% for ‘symptomatic disease’ – PHE and Canada

[64% in Israeli study: less effective
against symptomatic disease than against severe disease]



Pfizer, longer gap





PHE – Public Health England, May 2021. ‘Analysis of real-world data.’ Radio interview on Life Matters, Hilary Harper with Assoc. Prof. Margie Danchin, Murdoch Children’s Research Institute. (Monday 19 July 2021).

New England Journal of Medicine. ‘Nature’, article by Delphine Planas et al, 8 July 2021.

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