New editorial about the asymptomatic rate in Nature—the author of the preprint above are featured in this as well. They say asymptomatic and mild case rate might be up to 50% of all infections and that these people are infectious.
“Since severe cases, which more likely lead to fatal outcomes, are detected at a higher percentage than mild cases, the reported death rates are likely inflated in most countries. Such under-estimation can be attributed to under-sampling of infection cases and results in systematic death rate estimation biases. The method proposed here utilizes a benchmark country (South Korea) and its reported death rates in combination with population demographics to correct the reported COVID-19 case numbers. By applying a correction, we predict that the number of cases is highly under-reported in most countries. In the case of China, it is estimated that more than 700.000 cases of COVID-19 actually occurred instead of the confirmed 80,932 cases as of 3/13/2020.”
also implying a lower CFR than previously thought (perhaps less than 0.5%). 3k deaths in China / 700k actual cases)
With testing capacities of 20,000 tests daily, it [South Korea] has the largest and most accurate coverage compared to all other countries as of writing. The low false-negative rate in detecting COVID-19 infections leads to the lowest death rate compared to all other countries (0.84) with major case count
Note that South Korea’s reported (naive) CFR is at >1% by now. It’s possible that the authors adjusted for the fact that most of South Korea’s cases were still active at the time of writing (about 55-60% of cases are still active now, I think), but I don’t see this in this paper. It probably doesn’t make a huge difference, but still relevant that this could cause the estimates to be a bit too low.
This method requires the comparison of two countries with sufficient confirmed cases and reported deaths. One country (target country) will be adjusted, given the information from the second country (benchmark country). In order to adjust for the difference in the population demographics of the target country, T, and the benchmark country, B, we compute a Vulnerability Factor (VTB).
Am I right that they’re not factoring in that patients had worse prospects in Wuhan than in South Korea? I feel like whatever the outcome of their adjustment process, that value would need to be multiplied by a factor >1 which represents hospital overstrain in Hubei, where at least 60% of China’s numbers stem from (probably more but I haven’t looked it up). I don’t know how large that adjustment should be exactly, but I find it weird that there’s no discussion of this. Am missing something about the methodology (maybe it factors in such differences automatically somehow)?
Ah, OK: They list this as an assumption:
[Assumption]Treatment has minor influence on outcome The provided healthcare in countries is comparable. For developed countries such as Italy and South Korea, it is assumed that the population has similar access to treatment. The death rates reported by age group are thus applicable in all countries
This is important to keep in mind when we try to derive implications from their estimate. Especially if we look at the hospitalization rates estimated here on page 5. For this disease in particular where people sometimes have to stay in hospitals for several weeks, it’s hard to imagine that treatment only makes a small difference.
“The size of the COVID-19 reproduction number documented in the literature is relatively small. Our estimates indicate that R0= 26.5, in the case that the asymptomatic sub-population is accounted for. In this scenario, the peek of symptomatic infections is reached in 36 days with approximately 9.5% of the entire population showing symptoms, as shown in Figure 3.”
I think they estimate about 1 million severe cases in the US alone if left unchecked at the peak.
“It is unlikely that a pathogen that blankets the planet in three months can have a basic reproduction number in the vicinity of 3, as it has been reported in the literature (19–24). SARS-CoV-2 is probably among the most contagious pathogens known. Unlike the SARS-CoV epidemic in 2003 (25), where only symptomatic individuals were capable of transmitting the disease. Asymptomatic carriers of the COVID-19 virus are most likely capable of transmission to the same degree as symptomatic.”
“This study shows that the population of individuals with asymptomatic COVID-19 infections are driving the growth of the pandemic. The value of R0 we calculated is nearly one order of magnitude larger than the estimates that have been communicated in the literature up to this point in the development of the pandemic”
“DISCLAIMER: The following estimates were computed using 2010 US Census data with 2016 population projections and the percentages of clinical cases and mortality events reported in Mainland China by the Chinese Center for Disease Control as of February 11th, 2020. CCDC Weekly / Vol. 2 / No. 8, page 115, Table 1. The following estimates represent a worst-case scenario, which is unlikely to materialize. • Maximum number of symptomatic cases = 34,653,921 • Maximum number of mild cases = 28,035,022 • Maximum number of severe cases = 4,782,241 • Maximum number of critical cases = 1,628,734 • Maximum number of deaths = 3,439,516”
New editorial about the asymptomatic rate in Nature—the author of the preprint above are featured in this as well. They say asymptomatic and mild case rate might be up to 50% of all infections and that these people are infectious.
And another preprint saying there were +700k cases in China on 13th of March:
“Since severe cases, which more likely lead to fatal outcomes, are detected at a higher percentage than mild cases, the reported death rates are likely inflated in most countries. Such under-estimation can be attributed to under-sampling of infection cases and results in systematic death rate estimation biases. The method proposed here utilizes a benchmark country (South Korea) and its reported death rates in combination with population demographics to correct the reported COVID-19 case numbers. By applying a correction, we predict that the number of cases is highly under-reported in most countries. In the case of China, it is estimated that more than 700.000 cases of COVID-19 actually occurred instead of the confirmed 80,932 cases as of 3/13/2020.”
also implying a lower CFR than previously thought (perhaps less than 0.5%). 3k deaths in China / 700k actual cases)
From the paper:
Note that South Korea’s reported (naive) CFR is at >1% by now. It’s possible that the authors adjusted for the fact that most of South Korea’s cases were still active at the time of writing (about 55-60% of cases are still active now, I think), but I don’t see this in this paper. It probably doesn’t make a huge difference, but still relevant that this could cause the estimates to be a bit too low.
From the paper:
Am I right that they’re not factoring in that patients had worse prospects in Wuhan than in South Korea? I feel like whatever the outcome of their adjustment process, that value would need to be multiplied by a factor >1 which represents hospital overstrain in Hubei, where at least 60% of China’s numbers stem from (probably more but I haven’t looked it up). I don’t know how large that adjustment should be exactly, but I find it weird that there’s no discussion of this. Am missing something about the methodology (maybe it factors in such differences automatically somehow)?
Ah, OK: They list this as an assumption:
This is important to keep in mind when we try to derive implications from their estimate. Especially if we look at the hospitalization rates estimated here on page 5. For this disease in particular where people sometimes have to stay in hospitals for several weeks, it’s hard to imagine that treatment only makes a small difference.
And yet another preprint estimating the R0 to be 26.5:
Quotes from paper:
“The size of the COVID-19 reproduction number documented in the literature is relatively small. Our estimates indicate that R0= 26.5, in the case that the asymptomatic sub-population is accounted for. In this scenario, the peek of symptomatic infections is reached in 36 days with approximately 9.5% of the entire population showing symptoms, as shown in Figure 3.”
I think they estimate about 1 million severe cases in the US alone if left unchecked at the peak.
“It is unlikely that a pathogen that blankets the planet in three months can have a basic reproduction number in the vicinity of 3, as it has been reported in the literature (19–24). SARS-CoV-2 is probably among the most contagious pathogens known. Unlike the SARS-CoV epidemic in 2003 (25), where only symptomatic individuals were capable of transmitting the disease. Asymptomatic carriers of the COVID-19 virus are most likely capable of transmission to the same degree as symptomatic.”
“This study shows that the population of individuals with asymptomatic COVID-19 infections are driving the growth of the pandemic. The value of R0 we calculated is nearly one order of magnitude larger than the estimates that have been communicated in the literature up to this point in the development of the pandemic”
from supplementary materials:
“DISCLAIMER: The following estimates were computed using 2010 US Census data with 2016 population projections and the percentages of clinical cases and mortality events reported in Mainland China by the Chinese Center for Disease Control as of February 11th, 2020. CCDC Weekly / Vol. 2 / No. 8, page 115, Table 1. The following estimates represent a worst-case scenario, which is unlikely to materialize. • Maximum number of symptomatic cases = 34,653,921 • Maximum number of mild cases = 28,035,022 • Maximum number of severe cases = 4,782,241 • Maximum number of critical cases = 1,628,734 • Maximum number of deaths = 3,439,516”
https://drive.google.com/drive/folders/18qaRKnQG1GoXamnzJwkHu2GG9xCe4w8_