April 8 (UPI) -- China's aggressive control measures appear to have stopped the first wave of the COVID-19 outbreak in areas outside Hubei province, the epicenter of the global pandemic, an analysis published Wednesday in The Lancet suggests.
The average number of cases generated by a single infected individual during the outbreak fell substantially after China's measures were introduced on Jan. 23, and has remained below 1 ever since, according to the new modeling study by researchers at the University of Hong Kong.
This indicates that the epidemic has shifted from one that is growing rapidly to one that is slowly shrinking, the researcher report.
Given the significant risk of the virus being re-introduced from abroad, and with economic activity increasing, real-time monitoring of COVID-19 transmission and severity is needed to protect against a possible second wave of infection, the authors further emphasize.
"While these control measures appear to have reduced the number of infections to very low levels, without herd immunity against COVID-19, cases could easily re-surge as businesses, factory operations and schools gradually resume and increase social mixing, particularly given the increasing risk of imported cases from overseas as COVID-19 continues to spread globally," Dr. Joseph T. Wu said in a press release.
"Although control policies such as physical distancing and behavioral change are likely to be maintained for some time, proactively striking a balance between resuming economic activities and keeping the reproductive number below one is likely to be the best strategy until effective vaccines become widely available," he added.
Wu and his colleagues analyzed local Health Commission data of confirmed COVID-19 cases between mid-January and February 29 to estimate the transmissibility and severity of the virus in four major cities -- Beijing, Shanghai, Shenzhen, Wenzhou -- and 10 provinces outside Hubei with the highest number of confirmed case.
The number of new daily imported and local cases were used to construct epidemic curves for each location by date of symptom onset, with reporting delays factored in. The researchers also modeled the potential impact of relaxing control measures after the first wave of infection for different scenarios with rising transmission numbers.
The analyses suggest that in regions outside Hubei, control measures should be lifted gradually so that the resulting reproductive number does not exceed 1, or the number of cases will progressively rise.
The estimates also suggest that once elevated, simply tightening control interventions again would not reduce the burden back to its original level and would require extra effort to revert to pre-relaxation levels -- likely resulting in both higher health and economic loss.
"We are acutely aware that as economic activity increases across China in the coming weeks, local or imported infection could lead to a resurgence of transmission," said study co-author Dr. Kathy Leung. "Real-time monitoring of the effect of increased mobility and social mixing on COVID-19 transmissibility could allow policymakers to fine-tune control measures to interrupt transmission and minimize the impact of a possible second wave of infections."
Further analysis suggests that the confirmed case fatality rate outside Hubei was just under 1 percent, much lower than it was in the pandemic's epicenter, where nearly 6 percent of confirmed cases ended in death. Among the 10 provinces with the largest number of confirmed cases, case fatality ranged from 0 percent in prosperous regions to 1.76 percent in less-developed provinces.
China has been gradually lifting control measures in several provinces since February 17 and factories and offices are gradually reopening.
The authors believe their findings are critical to helping countries currently battling the outbreak understand when it is safe to relax control measures.
"Even in the most prosperous and well-resourced mega-cities like Beijing and Shanghai, health-care resources are finite, and services will struggle with a sudden increase in demand," said study co-author Dr. Gabriel M Leung. "Our findings highlight the importance of ensuring that local health-care systems have adequate staffing and resources to minimize COVID-related deaths."