I notice that the estimates of serial interval (almost?) all come from places that had pretty aggressive & successful containment measures in place, such as identifying & isolating potential carriers (including people who show symptoms, traced contacts, and high-risk travelers). That would tend to shorten the serial interval, since people who are identified early in their infection lose the opportunity to transmit during the later portion of their illness.
Are there estimates of what R was for these populations? If it’s a lot less than the 2-3 that other studies have found that would be some evidence that a lot of later-stage transmissions were prevented.
I was looking at this paper (for other reasons) and saw that it estimated a mean serial interval of 6.3 days in Shenzhen while there was aggressive testing, contact tracing, and isolating. They report that the mean serial interval was 3.6 days among patients who were infected by someone who was isolated within 2 days of symptom onset, and 8.1 days among patients who were infected by someone who wasn’t isolated until 3+ days after symptom onset, for an overall average serial interval of 6.3 in their population. They found R=0.4 - an average of 0.4 known transmissions from each infected person.
Insofar as the virus mostly spreads through presymptomatic transmission in some countries, that’s almost certainly because the people with symptoms are all isolated. Symptomatic people definitely spread the disease.
It’d be interesting if the R of these populations were <1 at the time the studies were done, though. If so, presymptomatic transmission might be insufficient to sustain exponential growth, as long as all symptomatic transmission is prevented.
Tapiwa Ganyani et al, the one with quantitative estimates of presymptomatic transmission, used data from Singapore up to Feb 26th and Tianjin up to Feb 27th. Both are cities which seem to have achieved containment over the relevant time period. I’m going to focus on Singapore, because information about what Singapore has been doing is easier to come by.
This article has a graph of Singapore’s case counts over the relevant time period, and appears to show it as being contained (R<1) during the relevant time period. This paper estimates the latency between people becoming symptomatic and being isolated in Singapore, and finds that it’s about 3 days for local cases as of Feb 26th, but longer on earlier dates. Their endpoint is “hospitalization or quarantine”, but reading Singapore’s FAQ, it sounds like they have a tiered system with two lesser levels of isolation that the paper doesn’t mention: leave of absence (advice to isolate with no legal force) and stay-home notice (which has legal force against leaving the house, but only a non-binding advisory against having visitors). The lesser isolation tiers are for traced contacts, and would be effective at preventing asymptomatic transmission as well.
My impression from all this is that Singapore’s measures would have driven symptomatic transmission down more than asymptomatic transmission, but substantially driven down both.
I notice that the estimates of serial interval (almost?) all come from places that had pretty aggressive & successful containment measures in place, such as identifying & isolating potential carriers (including people who show symptoms, traced contacts, and high-risk travelers). That would tend to shorten the serial interval, since people who are identified early in their infection lose the opportunity to transmit during the later portion of their illness.
Are there estimates of what R was for these populations? If it’s a lot less than the 2-3 that other studies have found that would be some evidence that a lot of later-stage transmissions were prevented.
I was looking at this paper (for other reasons) and saw that it estimated a mean serial interval of 6.3 days in Shenzhen while there was aggressive testing, contact tracing, and isolating. They report that the mean serial interval was 3.6 days among patients who were infected by someone who was isolated within 2 days of symptom onset, and 8.1 days among patients who were infected by someone who wasn’t isolated until 3+ days after symptom onset, for an overall average serial interval of 6.3 in their population. They found R=0.4 - an average of 0.4 known transmissions from each infected person.
Insofar as the virus mostly spreads through presymptomatic transmission in some countries, that’s almost certainly because the people with symptoms are all isolated. Symptomatic people definitely spread the disease.
It’d be interesting if the R of these populations were <1 at the time the studies were done, though. If so, presymptomatic transmission might be insufficient to sustain exponential growth, as long as all symptomatic transmission is prevented.
Tapiwa Ganyani et al, the one with quantitative estimates of presymptomatic transmission, used data from Singapore up to Feb 26th and Tianjin up to Feb 27th. Both are cities which seem to have achieved containment over the relevant time period. I’m going to focus on Singapore, because information about what Singapore has been doing is easier to come by.
This article has a graph of Singapore’s case counts over the relevant time period, and appears to show it as being contained (R<1) during the relevant time period. This paper estimates the latency between people becoming symptomatic and being isolated in Singapore, and finds that it’s about 3 days for local cases as of Feb 26th, but longer on earlier dates. Their endpoint is “hospitalization or quarantine”, but reading Singapore’s FAQ, it sounds like they have a tiered system with two lesser levels of isolation that the paper doesn’t mention: leave of absence (advice to isolate with no legal force) and stay-home notice (which has legal force against leaving the house, but only a non-binding advisory against having visitors). The lesser isolation tiers are for traced contacts, and would be effective at preventing asymptomatic transmission as well.
My impression from all this is that Singapore’s measures would have driven symptomatic transmission down more than asymptomatic transmission, but substantially driven down both.