On April 8, the city of Wuhan, the epicenter of the Covid-19 pandemic, ended its two-month mandatory confinement period. Nevertheless, China remains concerned about new outbreaks, driven by imported cases or asymptomatic patients. Is this fear justified or exaggerated?
It seems that China has finally managed to contain the Covid-19 epidemic. After 77 days of harsh confinement, the city of Wuhan, the epicenter of a global pandemic, reopened its doors on 8 April and residents were able to leave their homes and move around under strict conditions. The schools reopened in the second half of April. Since the start of the epidemic more than 82,000 cases have been recorded in Mainland China, including 4,600 deaths. On Tuesday 21 April, only 11 new cases were registered. By comparison, the US has 792,938 cases of Covid-19 and 42,518 people have died since the beginning of the epidemic.
78% of new cases are imported
But is china at risk of a second wave after deconfinement? On Tuesday 21 April, 11 new Covid-19 contamination cases were announced. Heilongjiang province, in the northeast of the country, is a matter of concern. In order to prevent further outbreaks of the epidemic, China closed its border with Russia but maintains a checkpoint in Suifenhe. As a result, Suifenhe imposed restrictions on 70,000 inhabitants and now only one person from each household can go shopping every three days. The local authorities have also converted the administration building into a field hospital that can accommodate 600 patients. The border with Burma has also been closely monitored, with several confirmed cases. Police and border guards have been deployed near the port of Lincang, where several hundred people tried to cross the border illegally.
Asymptomatic patients new fear of authorities
The second problem concerns asymptomatic cases, i.e. cases that are carriers of the virus but do not show symptoms of Covid-19 (cough, fever, breathing difficulties…). Since 28 January, a total of 6,800 asymptomatic cases have been registered, or 8% of cases, but this figure is largely underestimated due to a lack of testing. According to an article published in the British Medical Journal on 2 April, four out of five cases of the coronavirus in China are asymptomatic. These data are anecdotal and questionable but have led the Wuhan authorities to forcefully confine 70 of the 7,000 residential areas after the discovery of asymptomatic carriers. To measure this phenomenon, China has started an extensive investigation into nine regions, the official China Daily newspaper announced.
Drastic conditions for the movement of people
Since 8 April, over one million people have left or arrived in Wuhan under strict conditions, more than 93,000 trips a day. Only travelers with a negative serological test for the virus can buy a train ticket to Beijing. Upon arrival, they are subject to an additional 14-day quarantine. But even these draconian measures do not give a 100% guarantee. On Tuesday, the official TV channel CCTV reported a case of a Chinese man returning from the United States whose symptoms appeared two days after arrival despite a negative test result.
However, “it is not possible to keep the restriction forever,” said Zhong Nanshan, one of the experts advising the Chinese government. “It is normal to have a renewal after a major epidemic because the virus cannot be completely eradicated in such a short time”, confirms Yu Kaijiang, head of the Covid-19 treatment expert group in Suifenhe. The Chinese seem particularly suspicious. The second wave has not reached China but is present in everyone’s mind.
China has taken extreme measures to protect its population. Scientists published an assessment of the transmission and severity of Covid-19 during the first wave in The Lancet magazine and provided information on the parameters to be monitored to predict the likely second wave.
Wuhan has just come out of isolation after the first wave of the epidemic, which killed thousands of people. By slowly reopening, which is essential for the country’s economy and mental health, China is exposing itself to a second wave of the epidemic. On the one hand, due to imported cases now that the epidemic is global, and on the other hand, due to asymptomatic cases which are still contagious and about which little information is available. How will China have to prepare itself and what can we learn from its situation?
Useful drastic measures
The measures taken by China during the first wave of the SARS-CoV-2 outbreak were very useful in reducing the number of deaths. After the introduction of the drastic quarantine, the percentage of virus spread (RO) fell below 1 and serious cases in several Chinese provinces were 5 times lower.
However, now that it is reopening and the pandemic is global, China will have to consider a possible second wave of the epidemic. In fact, more cases may be imported and the epidemic may re-ignite because the containment and lack of vaccine have prevented the development of the herd’s immunity. Mass testing should continue to detect other potentially asymptomatic cases. This gives a picture of what deconfinement will look like in the US. Finally, in order to prepare for this likely second wave, China, like any other country at the time of deconfinement, will have to monitor the two parameters very closely: Ro and the percentage of serious cases.
Monitoring R0 and serious cases
These are the two main indicators that need to be closely monitored so that drastic measures can be taken if necessary. If Ro rises above 1 again, the epidemic will spread again and wreak havoc. Note that during the Spanish flu, it was the second wave that caused most deaths. The number of serious cases is also important: if the epidemic continues to circulate, but vulnerable people remain confined (and therefore unaffected) hospitals will be less overwhelmed. This is an important factor to take into account when considering a strategy for a possible second wave in order to achieve an optimal balance between health and economic protection.
Covid-19: how to slow down the second wave of the epidemic?
While the US is only at the beginning of the containment process, China has already lifted the restrictions after over two months of quarantine. This raises the important question of how to return to normal without risking a second wave? A study published in The Lancet tested several scenarios, including one that would save two months.
In the Chinese province of Hubei, the inhabitants have already returned to normal life after more than two months of quarantine and they are able to move as they see fit as long as they do not show any symptoms of Covid-1.
Research in The Lancet has simulated the impact of a sudden or gradual increase in isolation on the time and size of this second wave. It proposed to maintain the measures for another month so that the second peak of the epidemic would be delayed by two months.
The computer simulation yielded these predictions. It is based on a comparative epidemiological model called « susceptible-exposed-infectious-removed », (SEIR) which is often used to estimate the number of infected people. For each measure of social distance, such as company and school closures, the simulation predicted the number of infected people as a function of time.
The results suggest that if these preventive measures were lifted in March, a second wave of the epidemic could already occur at the end of August. Conversely, maintaining these measures until April would delay the second peak of the epidemic by two months. The second wave will not arrive until October, giving the health infrastructure time to breathe and prepare.
The gradual easing of restrictions could slow down and reduce the severity of the second peak.
“The unprecedented measures taken in Wuhan to reduce social contact at school and at work have helped to contain the epidemic”. says Kiesha Prem of the London School of Hygiene & Tropical Medicine, who conducted the study. Now, however, the city needs to be very careful about abolishing social distancing measures prematurely, as this could lead to an earlier second peak. But if they gradually alleviate the restrictions, this could slow down the return and reduce the severity of the peak.
A limited study, but valuable results
Like all simulations, this one has its limits. Scientists have deliberately decided that children are just as contagious as adults in order to simplify the calculations. Moreover, the same basic reproduction rate (RO) was used in all cases. So superspreaders that can infect many more people than the average RO have not been taken into account. Although the results may not apply to all countries as it is based on the data available for Wuhan, they offer an interesting view of how the second wave of the epidemic can be reduced. It can help governments and authorities make decisions about post-crisis management.
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