rtnew=1.7 is an entirely different case. Suppressing it would require the sort of lockdown that would yield rt=0.6 for the old strain,
Is this valid reasoning? Intuitively I’d expect current measures to be more effective for a more infectious strain, so that it would require a lockdown that would yield something closer to 0.8 for the old strain.
I suspect that some measures will remain close to 100% effective, like not seeing family members and friends. Similarly some things physically can’t become more infective, like being infected by your partner.
In that case I would expect that what currently are very high risk interactions (e.g. partner) and very low risk interactions (e.g. masked, 6ft+ grocery shopping) will still be almost as risky for a more infectious strain.
However if the bulk of infections happen because of moderate risk interactions, then moderate risk interactions becoming high risk interactions would significantly increase overal cases.
I wonder if the sudden increase is not just the result of some holiday or cold weather some time before. What are the chances that a new strain would dramatically increase daily cases in two countries within a few days of each other. Notably it started to increase in the Netherlands a few days before the UK. If anything this would point to it coming from a third country, yet it would still be odd that the outbreaks progress roughly in the same manner.