The UK government has stated that "Short-term vaccine efficacy from the first dose of the Pfizer-BioNTech vaccine is calculated at around 90%" and therefore "Given the high level of protection afforded by the first dose, models suggest that initially vaccinating a greater number of people with a single dose will prevent more deaths and hospitalisations than vaccinating a smaller number of people with 2 doses".
Which all seems, well, pretty sensible actually. So why have the WHO, Pfizer, Dr Fauci (head of the US department that deals with infectious diseases) and some other vaccine specialists said they don't recommend it?*
If we look at the Pfizer data, they did dosing tests**. 10µg, 30µg, and 100µg. The last of which they did only one dose of (possibly to test if this could be a one-dose vaccine). The second dose is given on day 21 (for the 10µg and 30µg doses), so we can see the results on day 28 of giving a second dose. The numbers are the immunogen concentrations.
Here are the results.
|Day 7||Day 21||Day 28||Day 35|
And if you look at that, you can see that a week after the second dose the first two trials are looking great - they result of the second dose is that immunogenicity skyrockets. The results of not giving a second dose is that it...drops. They didn't bother with testing those people at day 35. Presumably because it was clear that two doses were needed.
So if we're dependent on the second dosage, why do the UK government think that 90% is going to be achieved from dosage 1? Turns out it's because they've looked at the figures in the Stage 3 study***, where it says that during the week *after* the second dose is given the efficacy is 90%, and assumed that because it's so soon after the second dose is given, that the second dose can't be responsible, that those figures must be what you'd get without it. But for the 30µg dose (which that graph is for) the immnogenicity shoots up from 1,500 to 27,800 (almost 20 times!) during that week! I can't see how that couldn't easily be responsible for the increase of immunity from 50% to 90%.
So, frankly, I'm finding myself very sceptical about the government's line there. And I would like someone to reassure me that I'm misunderstanding in some way.
To be clear - if you get offered a vaccine, take it. Any immunity is better than none, and it might still be better to cover the country with 50% immunity than to give half the country 95% immunity. But I am very troubled that the government's advice isn't adding up.
(Many thanks to Kenny, whose thread on this started me digging to reassure myself.)
*Some have also come out in favour of it. It's by no means a wash.
**Pfizer Stage 1/2 study. All numbers are from Figure 4.
***Pfizer stage 3 study. The important bit is Figure 3, which compares immunity on different dates.
Original post on Dreamwidth - there are comments there.