We’ve produced our latest estimates for the level of #COVID19 infection rates across the UK https://t.co/P5acjH4kNg pic.twitter.com/uyCKU11Wjv
— Office for National Statistics (ONS) (@ONS) January 22, 2021
Really interesting stuff from the UK here.
You may recall that I posted an article evaluating four hypothetical mechanisms by which B.1.1.7 might get its increased transmission. From memory, I think they were a) higher infectivity overall (more virus produced or virus more effective at infecting, b) better spread in children, c) better able to reinfect "immune" people, d) faster generation time, i.e. 4 days instead of 6 per new infection.
At the time, (a) fit the data best. But one of the predictions was that if (d) was part or all of the answer, a consequence would be B.1.1.7 dropping its share of the new infections if a lockdown reduced Rt below 1.0.
Well, Rt is below 1.0 ... and B.1.1.7's share is dropping in all regions of the UK. It would take some concerted contact tracing and analysis to determine the average generation time, but this is the signature you'd expect if it go its boost largely through reaching the infectious stage earlier. (This would actually be expected given the changes to the spike and the increased viral loads.)
"Serial interval" is the average time between steps in a transmission chain. It was estimated around 5.5 to 6 days, but if B.1.1.7 is just as contagious but reduced that to 4 or 4.5, that would drive a huge increase. But paradoxically, in a lockdown environment, faster life cycles mean faster drops. Doesn't seem entirely intuitive to me, but that paper a few weeks ago was really well done.
UK press briefing has suggested a potential increase in mortality from the B.1.1.7 strain. How much? Supposedly about 30% more lethal than the original. All preliminary at this point.
Another unknown is on the efficacy of the current vaccines in lieu of the new strains. Using serum taken from vaccinated people, it appears to be very good at neutralizing the South African variant. Significant, because there is valid scientific concern that it might be resistant to some extent.