For personal reasons it made sense for me to calculate the percentage of Londoners who will have COVID this Thursday, the 16th. The number I got was much higher than I intuitively expected: 10%. Please point out any errors you see!
Among specimens collected in London 5 days ago, about 8000 were positive. This is relative to 4000 before the recent rise in cases, suggesting about 4000 are Omicron. Source
Omicron doubles at a rate of 2.5 days in the UK. Source
So among specimens collected Monday, we’d expect ~16k Omicron cases. Among specimens collected Thursday the 16th that should be ~35k.
As a ballpark guess, we might guess that about half of cases are caught, so that’s ~70k.
The typical time period between someone catching COVID and getting tested is 5 days. So the number of Londoners who will catch COVID on Thursday is ~280k, since they’ll typically get tested 5 days (two doublings) after that. That’s about 3% of the population of London.
Omicron grows by a factor of ~1.3 per day, so (3/1.3)% will catch COVID on Wednesday, and so on. The total percentage of Londoners who will have COVID on Thursday is thus ~10% (summing the appropriate geometric series).
For reference, the Zoe symptoms app project estimates around 1.3-2% prevalence of symptomatic Covid for London burrows: https://covid.joinzoe.com/data
I think asymptomatic cases are maybe 40%? Have seen it be a bit higher, but I doubt the higher numbers for asymptomatic cases. Going with 50% asymptomatic, this would indicate prevalence of 2.6-4%. That’s for today. Your estimate is 2 days in the future, so plausible but maybe a bit high?
Under the assumption that Omicron is 50% of cases today, and doubling time 2.5 days, maybe that would give 5-6% on the 16th.
For personal reasons it made sense for me to calculate the percentage of Londoners who will have COVID this Thursday, the 16th. The number I got was much higher than I intuitively expected: 10%. Please point out any errors you see!
Among specimens collected in London 5 days ago, about 8000 were positive. This is relative to 4000 before the recent rise in cases, suggesting about 4000 are Omicron. Source
Omicron doubles at a rate of 2.5 days in the UK. Source
So among specimens collected Monday, we’d expect ~16k Omicron cases. Among specimens collected Thursday the 16th that should be ~35k.
As a ballpark guess, we might guess that about half of cases are caught, so that’s ~70k.
The typical time period between someone catching COVID and getting tested is 5 days. So the number of Londoners who will catch COVID on Thursday is ~280k, since they’ll typically get tested 5 days (two doublings) after that. That’s about 3% of the population of London.
Omicron grows by a factor of ~1.3 per day, so (3/1.3)% will catch COVID on Wednesday, and so on. The total percentage of Londoners who will have COVID on Thursday is thus ~10% (summing the appropriate geometric series).
Thoughts?
For reference, the Zoe symptoms app project estimates around 1.3-2% prevalence of symptomatic Covid for London burrows: https://covid.joinzoe.com/data
I think asymptomatic cases are maybe 40%? Have seen it be a bit higher, but I doubt the higher numbers for asymptomatic cases. Going with 50% asymptomatic, this would indicate prevalence of 2.6-4%. That’s for today. Your estimate is 2 days in the future, so plausible but maybe a bit high?
Under the assumption that Omicron is 50% of cases today, and doubling time 2.5 days, maybe that would give 5-6% on the 16th.
R0 will go down a bit as more people become immune to Omicron, but...sure.