A preprint posted on Friday on medRxiv suggests that the heroic countermeasures undertaken in Wuhan have worked far better than had been predicted in the West, where quarantine has long been out of ideological favor. The rising blue line is the predicted number of new ascertained cases in Wuhan after February 1, while the falling Xs are the actual ascertained cases.
Evolving Epidemiology and Impact of Non-pharmaceutical Interventions on the Outbreak of Coronavirus Disease 2019 in Wuhan, China
View ORCID ProfileChaolong Wang, Li Liu, Xingjie Hao, Huan Guo, Qi Wang, Jiao Huang, Na He, Hongjie Yu, Xihong Lin, View ORCID ProfileAn Pan, Sheng Wei, Tangchun Wu
This article is a preprint and has not been peer-reviewed. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.
BACKGROUND We described the epidemiological features of the coronavirus disease 2019 (Covid-19) outbreak, and evaluated the impact of non-pharmaceutical interventions on the epidemic in Wuhan, China. METHODS Individual-level data on 25,961 laboratory-confirmed Covid-19 cases reported through February 18, 2020 were extracted from the municipal Notifiable Disease Report System. Based on key events and interventions, we divided the epidemic into four periods: before January 11, January 11-22, January 23 – February 1, and February 2-18. We compared epidemiological characteristics across periods and different demographic groups. We developed a susceptible-exposed-infectious-recovered model to study the epidemic and evaluate the impact of interventions. RESULTS The median age of the cases was 57 years and 50.3% were women.
Men and women were hit about equally, although men somewhat more severely. In China, men are much more likely to be smokers, so the difference in smoking rates didn’t seem to hugely matter. So, don’t assume that this is dangerous only to Bad People Who Smoke.
The attack rate peaked in the third period and substantially declined afterwards across geographic regions, sex and age groups, except for children (age <20) whose attack rate continued to increase. Healthcare workers and elderly people had higher attack rates and severity risk increased with age. The effective reproductive number dropped from 3.86 (95% credible interval 3.74 to 3.97) before interventions to 0.32 (0.28 to 0.37) post interventions.
Before the Wuhan lockdown, each case was creating an average of 3.86 new cases, which was very, very bad. After the lockdown, R-nought fell to 0.32. An R-nought above one means it’s spreading, below one it’s shrinking. The 1918 Spanish Flu is usually estimated to have been around 2.
But what happens when Wuhan reopens for business?
The interventions were estimated to prevent 94.5% (93.7 to 95.2%) infections till February 18. We found that at least 59% of infected cases were unascertained in Wuhan, potentially including asymptomatic and mild-symptomatic cases. CONCLUSIONS Considerable countermeasures have effectively controlled the Covid-19 outbreak in Wuhan. Special efforts are needed to protect vulnerable populations, including healthcare workers, elderly and children. Estimation of unascertained cases has important implications on continuing surveillance and interventions. …
Here’s the PDF of the full article with graphs.
A total of 1316 healthcare workers were infected, representing 5.1% of the total cases (Table 1). The average attack rate in local healthcare workers (144.7 per 106 people; 95% CI, 137.0 to 152.8) was substantially higher than that in the general population (41.7 per 106 people; 41.2 to 42.2) overall, and particularly in the third period (507.4 per 106 people; 468.6 to 548.5; Fig. 3A).
Health care workers were almost 3.5 times as likely as general public to be infected.
Strikingly, we estimated that the overall ascertainment rate was 0.21 (95% CrI, 0.18-0.24), and similar across the periods (Table S2). We predicted the cumulative number of ascertained cases to be 26,252 (95% CrI, 23,116 to 29,522) by February 18, close to the actual reported number of 25,961, while the estimated cumulative number of total cases was 125,959 (105,060 to 151,612). Our model suggested the number of active infectious cases in Wuhan peaked on February 1, and then gradually dropped afterwards (Fig. 4E). If the trend remained unchanged, we predicted the number of ascertained cases to become zero by April 22 (95% CrI, April 5 to May 19), 2020, and the total number of both ascertained and unascertained cases would become zero around May 4 (April 17 to May 30), 2020.
In 1918, many U.S. cities were hit with a double whammy.
The attack rate continued to increase before February 2 while dramatically declined thereafter for all groups, except for children (age <20 years). Consistent with early analyses, younger people were less likely to be affected,8,11,21 but we found that the attack rate continued to increase over time for those aged under 20 years. In particularly, infants under the age of 1 year had the highest attack rate than the other age groups of children, probably because they cannot wear masks and have low immunity.22 Children had a lower chance of getting infected probably because they had less frequent social activities during the school winter break starting in early or middle January, but the attack rate increased when all people were required to stay at home and risk of familial clustering of infection started to increase.11 Our results also indicated that healthcare workers and elderly people had higher attack rates and the severity increased significantly with age. Therefore, special attention and efforts should be applied to protect and reduce transmission and progression in vulnerable populations including healthcare workers, elderly people and children.
Here’s an important question: children are much less likely to be “ascertained” as infected?
But … the majority of cases are assumed by these researchers to be unascertained. Are unascertained cases (most of them only mildly symptomatic or nonsymptomatic) as infectious as ascertained cases? Are children less likely to be infected or just less likely to be symptomatic and thus ascertained? How infectious are children to each other and to adults?
These are important questions for whether to close the schools or not. Similarly, should blockbuster movies aiming at young audiences not be released into theaters?