Yeah 7 days was intended to be a reasonable conservative guess. My actual guess is closer to 5.5. As you point out there are testing artifacts that point in both directions. Within china, test shortages, outside of china, slower testing roll out. I’m not an epi expert but I think the gold standard here would be to do something like time-series immune surveillance, where you randomly sample a large group of people from a pop and test them for an antibody reaction and/ or viral RNA, then do the same at intervals later. My guess is this is challenging because of the number of samples required to detect in most places, but maybe if you did this somewhere like italy you could pull it off (you get the population abundance as well).
Its also the case that this isn’t a fixed number, and you expect it to vary from population to population based on fraction of asymptomatic cases, social distancing, pop density etc. So I’m not sure we’ll get a better number than 2-8 days in the short term, which is disconcerting given how big of a difference it makes to risk forecasts.
I’d love to hear from anyone with more epi expertise!
Yeah 7 days was intended to be a reasonable conservative guess. My actual guess is closer to 5.5. As you point out there are testing artifacts that point in both directions. Within china, test shortages, outside of china, slower testing roll out. I’m not an epi expert but I think the gold standard here would be to do something like time-series immune surveillance, where you randomly sample a large group of people from a pop and test them for an antibody reaction and/ or viral RNA, then do the same at intervals later. My guess is this is challenging because of the number of samples required to detect in most places, but maybe if you did this somewhere like italy you could pull it off (you get the population abundance as well).
Its also the case that this isn’t a fixed number, and you expect it to vary from population to population based on fraction of asymptomatic cases, social distancing, pop density etc. So I’m not sure we’ll get a better number than 2-8 days in the short term, which is disconcerting given how big of a difference it makes to risk forecasts.
I’d love to hear from anyone with more epi expertise!
Related- possibly first use of immune surveillance: https://www.sciencemag.org/news/2020/02/singapore-claims-first-use-antibody-test-track-coronavirus-infections