On the question of one dose or two for the COVID vaccines. I think it's the right call to delay the 2nd dose from 3 weeks to ~12. Concerns from GPs and others are perfectly reasonable, but data presented in short JCVI report support it 1/10 https://www.cas.mhra.gov.uk/ViewandAcknowledgment/ViewAttachment.aspx?Attachment_id=103741

At 10 days, Pfizer vaccine's effect becoming measurable. Fig 1 JCVI report. Pfizer's own number for Vaccine Efficiency=52% would worry you at first look but really isn't as low as that. 52% comes from calculating from day 1 to 21. But takes 10 days for body to respond 2/10

52% is not incorrect, but it absolutely does not represent the true Vaccine Efficiency (VE) after 1 dose. Calculating VE between 10-21 days is the method that best represents the vaccine's effect. That is 89%. It's very clear - blue line diverges from red at 10days. 3/10

So already, at 10-21 days (before 2nd dose), 89% efficiency is measured. That is measured, not inferred, or guessed, measured. You may argue about the error on it (52 - 97% for 95% confidence limit), but it is a defensible (simple) calculation. 4/10

Now this is really what the JCVI are dealing with - there are no measurements beyond 21-28 days for single dose Pfizer. The 2nd dose probably takes 7 days to kick in (hence the 21-28d I use). There is uncertainty, but we live with uncertainty and risk. 5/10

The risk is we don't have measurements beyond 21-28 days to say if VE will remain at about 89%. In the expert opinion of the JCVI, it is extremely unlikely this will drop to zero fast. What happens between 28 and 84 days (the new 12 week 2nd dose) is the key. 6/10

In face of rapidly spreading new variant, wearisome public that overall is not as strict with distancing measures as in t April 2020 lockdown (people get both fed up and complacent). And the fall out of Xmas mixing. And limited vaccine supply What is the right call ? 7/10

I think delaying 2nd dose for 12 weeks is probably the right tack. Immune response may wane 28-84 days, but how fast? Unknown, but very unlikely to go to zero in view of vaccine experts. Note - JCVI judgement WAS based on data, measurement, and their scientific acumen. 8/10

Moderna shows similar results. The JCVI report does not have a similar plot for Oxford- Astrazeneca but quotes an unpublished and exploratory analysis of 1 dose participants. It appears to be at least 73% after 22 days up to (I think) 84 days. 9/10

Appreciate GP and primary care concerns, patient trust important, communication with public vital. But efficacy of the vaccine programme must win out. Science has not changed, numbers have not been massaged. It's just fast moving, we should be prepared for more moves. 10/10