The R0 of Delta is ca. 2x the R0 of the Wuhan strain and this doubles the effect of new immunity on Rt.
In fact, the ONS data gives me that ~7% of Scotland had Delta so that’s a reduction in Rt of R0*7% = 6*7% = 0.42 just from very recent and sudden natural immunity.
That’s not [edited: forgot to say “not”] enough to explain everything, but there are more factors:
1) Heterogenous immunity: the first people to become immune are often high-risk people who go to superspreader events etc.
2) Vaccinations also went up. E.g. if 5% of Scotland got vaccinated in the relevant period, and that gives a 50% protection against being infected or infecting others (conditional on being infected), that’s another reduction in Rt of ca. 6*0.05 = 0.18.
3) Cases were rising and that usually leads to behavior changes like staying at home, cancelling events, and doing more LFD tests at home.
The R0 of Delta is ca. 2x the R0 of the Wuhan strain and this doubles the effect of new immunity on Rt.
In fact, the ONS data gives me that ~7% of Scotland had Delta so that’s a reduction in Rt of R0*7% = 6*7% = 0.42 just from very recent and sudden natural immunity.
That’s not [edited: forgot to say “not”] enough to explain everything, but there are more factors:
1) Heterogenous immunity: the first people to become immune are often high-risk people who go to superspreader events etc.
2) Vaccinations also went up. E.g. if 5% of Scotland got vaccinated in the relevant period, and that gives a 50% protection against being infected or infecting others (conditional on being infected), that’s another reduction in Rt of ca. 6*0.05 = 0.18.
3) Cases were rising and that usually leads to behavior changes like staying at home, cancelling events, and doing more LFD tests at home.