Summary: A mathematical model using real-time monitoring of COVID-19 transmissibility and severity recommends carefully calibrated control strategies to reduce the risk of a second wave of infection in mainland China.
Source: The Lancet
New modelling published in The Lancet indicates that China’s stringent control measures appear to have suppressed the first wave of COVID-19 in regions outside Hubei province. Researchers warn, however, that the risk of reintroduction from abroad and increased social and economic activity mean continual monitoring of transmissibility and disease severity is essential to guard against a possible second wave.
The study estimates that, in areas outside Hubei, the instantaneous reproductive number (the average number of secondary cases produced by an infected person at a given time) fell sharply after lockdown measures began on 23 January 2020 and has remained below one since. This suggests the epidemic in those regions transitioned from rapid growth to a gradual decline.
Mathematical simulations in the study show that lifting control measures too early would likely raise the reproduction number above one again, triggering a renewed wave of transmission. The findings underscore the importance of carefully phased relaxation of interventions to prevent resurgence.
These insights are particularly relevant for countries still in the early stages of lockdown. The study did not evaluate the individual effect of each intervention or determine which specific measures were most effective, but it highlights the broader risk of premature easing across the board.
“While control measures have driven infections to very low levels, without population immunity COVID-19 can quickly resurge as businesses, factories and schools reopen and social mixing increases, especially with the risk of imported cases while the virus circulates internationally,” says Professor Joseph T. Wu of the University of Hong Kong, co-leader of the research.
He adds, “Measures such as physical distancing and changes in behaviour will likely be necessary for some time. Actively balancing the resumption of economic activity with maintaining a reproduction number below one is probably the most feasible strategy until effective vaccines are widely available.”
The analysis also examined disease severity. The confirmed case fatality risk—the probability of death among officially reported confirmed cases—was estimated at 0.98% outside Hubei, almost six times lower than the 5.91% reported in Hubei. Case fatality varied substantially across provinces, reflecting differences in economic development and health-care resources. Among the ten provinces with the most confirmed cases, fatality ranged from 0% in more prosperous regions such as Jiangsu to 1.76% in less developed provinces like Henan.
“Even in well-resourced megacities such as Beijing and Shanghai, health-care capacity is finite, and a sudden surge in demand would strain services,” says senior author Professor Gabriel M. Leung from the University of Hong Kong. “These results highlight the need to ensure local health systems have adequate staff and resources to minimise COVID-related deaths.”
Background: A novel coronavirus (SARS-CoV-2) emerged in Wuhan in December 2019 and spread across China. Nationwide restrictions on movement and commerce were introduced on 23 January. These measures have had major social and economic impacts. Since 17 February, several provinces have begun to relax restrictions and gradually reopen factories and offices.
Study methods: Researchers used local Health Commission data on confirmed COVID-19 cases from mid-January through 29 February 2020 to estimate transmissibility and severity in four major cities—Beijing, Shanghai, Shenzhen and Wenzhou—and in the ten provinces outside Hubei with the highest case counts. They constructed epidemic curves by date of symptom onset using counts of new daily imported and local cases, and incorporated reporting delays (the lag between symptom onset and case reporting) into their models to calculate weekly reproduction numbers. The team also modelled scenarios for relaxing control measures and the likely effect of rising reproduction numbers on transmission.
Key implications: The analyses indicate that control measures outside Hubei should be eased gradually so that the effective reproduction number remains at or below one; otherwise cases will begin to rise during the relaxation period. The authors note that once transmission increases, simply reimposing interventions may not quickly return case numbers to previous low levels. Reversing an upswing would require stronger effort to drive the reproduction number below one, with greater health and economic costs.
“As economic activity increases in the coming weeks, local or imported infections could trigger renewed transmission,” says co-lead author Dr Kathy Leung of the University of Hong Kong. “Real-time monitoring of how increased mobility and social mixing affect COVID-19 transmissibility will allow policymakers to fine-tune interventions and minimise the impact of a potential second wave.”
Limitations: The study’s reproduction number estimates rely on reported confirmed cases, and onset date information was unavailable for some provinces and substituted from Shenzhen data. The simulations of relaxed measures were limited in number and did not map specific interventions or public responses to each scenario.
In a linked Comment, Dr Shunqing Xu of Huazhong University of Science and Technology (not involved in the study) notes that confirmed case fatality rates varied with provincial per capita GDP and hospital bed availability. He reports a Wuhan CFR of up to 5.08% by 28 March 2020 and cautions that differences in health-care capacity should inform intervention planning.
Funding: The research was funded by the Health and Medical Research Fund, Hong Kong, China, and conducted by researchers at The University of Hong Kong.
About this coronavirus research article
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The Lancet
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Lancet Press Office – The Lancet
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Original Research: The full article “Beware of the second wave of COVID-19” is available from The Lancet.
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