I think the switch to 8 weeks was at least in part driven by the different characteristics of the Delta variant. Whereas for the previous variants the two doses of the vaccine did something like 70% and 90% protection, for the Delta variant it’s more like 35% and 80% (vague hand wavey numbers). So now there is similar marginal benefit to getting second doses into people, and because the roll out has been by age category, getting (say) 60-year olds from 1 dose to 2 might well be more beneficial than getting 20-year olds from 0 to 1.
It’s quite unclear to me why they not just switch the spike protein to the one of the Delta variant if that’s the main reason for chaing how they vaccinate.
Also, note that the UK recently decreased the time range from 12 weeks to 8 weeks: UK reduces gap between two covid vaccine doses from 12 weeks to 8 weeks (livemint.com).
I’m not clear on the reason, but they have vaccinated 80% of adults with 1st doses, so perhaps they’ve decided that the need for 1st doses is dropping: Vaccinations in the UK | Coronavirus in the UK (data.gov.uk).
I think the switch to 8 weeks was at least in part driven by the different characteristics of the Delta variant. Whereas for the previous variants the two doses of the vaccine did something like 70% and 90% protection, for the Delta variant it’s more like 35% and 80% (vague hand wavey numbers). So now there is similar marginal benefit to getting second doses into people, and because the roll out has been by age category, getting (say) 60-year olds from 1 dose to 2 might well be more beneficial than getting 20-year olds from 0 to 1.
It’s quite unclear to me why they not just switch the spike protein to the one of the Delta variant if that’s the main reason for chaing how they vaccinate.
That was my impression.