Reporter : He Liping
Publisher : The Paper, via ScienceNet
Direct translation
On July 16, local time, a modeling study published online by the top academic journal "Nature" showed that the public health intervention measures gradually adopted from January to March 2020 are multi-pronged, and Wuhan will end in March. The cumulative number of infections on the 8th decreased by 96.0%. At the same time, from January to March, up to 87% of COVID-19 cases may be undetected. Undetected or confirmed cases include asymptomatic, pre-symptomatic or mildly infected. These groups may have played an important role in the spread of the disease. If restrictions are lifted too early, this group will cause the epidemic to rebound.
The research was jointly completed by the research team of Huazhong University of Science and Technology and Harvard University. The research is entitled "Reconstruction of the full transmission dynamics of COVID-19 in Wuhan". The corresponding author is Huazhong University of Science and Technology. Professor Chaolong Wang of the Department of Epidemiology and Health Statistics of the School of Public Health and Professor Lin Xihong of the Department of Biostatistics at Harvard University and academician of the National Academy of Medicine.
Asymptomatic, pre-symptomatic or mild COVID-19 infections are considered to play an important role in the rapid spread of the disease, and they are generally difficult to find and isolate. The authors believe that the full dynamic reconstruction of the outbreak will help to better understand the proportion and impact of undiagnosed COVID-19 infections, and may be of reference value for the prevention and control of the resurgence of the epidemic.
Wang Chaolong and others studied the propagation dynamics of the COVID-19 outbreak in Wuhan and used 32,583 laboratory confirmed cases data from December 8, 2019 to March 8, 2020 to evaluate the effect of the intervention. They used these data to simulate the epidemic from January 1, 2020, and divided them into five periods based on key events and intervention measures, such as the Chinese New Year and the implementation of centralized quarantine.
The research team’s analysis showed that the initial transmission rate was very high. The basic reproduction number (R0) in the first stage was about 3.54, which dropped to about 0.28 in the final stage of the study. This result shows that the multi-pronged approach to public health interventions gradually taken from January to March 2020 reduced the cumulative number of infections in Wuhan as of March 8 by 96.0%.
The research team fitted their model with epidemiological data, proving that there may have been a large number of undetected cases in Wuhan. During the period of their study, it is estimated that 87% of the infection cases were undetected. Even under the extreme assumption that all cases were detected in the initial stage, the lower limit of this proportion was 53%.
The research team believes that public health interventions such as quarantine isolation and social alienation seem to be an effective means of blocking the transmission of undiagnosed cases and controlling the epidemic. They also emphasized that investigations such as serological studies should be carried out to confirm these estimates.
The research team also used the fitted model of these data to predict the probability of the second wave of outbreaks. Assuming that all restrictions are lifted on the 14th day after the first notification of no new cases, the probability of an epidemic rebound is expected to be very high, up to 97%, and the source of infection is mainly from undetected mild or asymptomatic cases. The number of cases is expected to increase sharply on the 34th day after the ban is lifted. Another stricter scenario assumes that all restrictions will not be lifted until there are no new cases for 14 consecutive days. At this time, the probability of rebound will drop to 32%, and the surge in cases will also be delayed until the 42nd day after lifting the ban.
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