Since the Delta variant (B.1.617.2) has a higher basic R number than even the Alpha variant (B.1.1.7) - how much larger is not yet clear
- and against which the available vaccines' effectiveness after 2 doses against infection is less, . . .
85% of adults (O/16) seems an optimistic figure for significant flock immunity effects to drop the effective R number below 1, on the assumption that no earlier than 21 Jun (and surely by mid July) the NPIs will be relaxed.
Behavioural changes will endure across the country (UK) without legal force. Ironically the sections and cohorts of the population who are least likely to be spreaders will be the ones who are most careful and the spreading element are the ones who will forget the threat (not just to them but to their community and wider constituency). I think it's likely that the Government will decide to go with the 21 Jun date, judging that the tests have been passed (but we have another few days of data to inform that decision: SAGE meets mid next week (
latest released minutes). On the table as a useful measure when the decision is made/announced (14 Jun) will be selective continued restraint on certain multi-person indoor activities likely to be high risk eg: night clubs and bars (standing: sitting and table service is lower risk), weddings larger than currently allowed. This sort of activity affects few, in practice, and the adverse effect on the economy of their continued proscription would be minimal.
On balance I reckon that this third wave (absolutely as predicted by the SPI-M modellers (I prefer the Warwick analysis and treatment - see below)) will endure to a peak in July and decay in August. As the vaccination percentage pushes up to 85% the decay gradient is likely to be steeper than the rise. Besides the (%) protection from vaccination, increasing numbers of the unvaccinated will catch COVID-19, mostly mild or asymptomatic, and their numbers can be added to the no longer susceptible total. Critically, the effect of mid-90% double vaccination of all over 50s and other vulnerable groups can be expected to delink case numbers with serious disease (proxy metric = hospital admissions) numbers.
This modelling was done in late March. One observation I'd make is that the model maintained (default) a higher linkage between cases and hospital admissions than I think the modelling presented to SAGE next week will use (we now have better data).