Commentary: Looks like containment of novel coronavirus not as effective as we had hoped
Critical differences between the epidemiology of the novel coronavirus and SARS make containment less effective as a strategy and mitigation more urgent, says Hitoshi Oshitani.
TOKYO: A novel coronavirus is rapidly spreading within China, with more cases discovered outside the country this past week.
The virus is genetically close to the Severe Acute Respiratory Syndrome (SARS) coronavirus , which caused a global outbreak in 2002 to 2003.
Despite their similarities, however, this new virus shares few epidemiological characteristics with SARS, which was successfully contained after causing more than 8,000 cases with 774 deaths worldwide.
This new virus may be more difficult to control than SARS. The number of cases has already exceeded the total number of cases of SARS – and in just one month.
It is likely that the Wuhan health authorities tried to contain the new virus using the same strategy previously used for the containment of SARS. However, containment by these means looks like an less effective means to deal with this new virus compared to SARS.
We have insufficient epidemiological data to understand the whole epidemiology of this novel coronavirus because we are still in the early stages of its spread.
At this time, however, we have seen some critical differences between the epidemiology of SARS and this virus that may make this much more difficult to manage than SARS.
HOW EFFECTIVE IS CONTAINMENT?
Active and comprehensive discovery of infected individuals, rapid isolation of cases, and identification of all close contacts by contact tracing were the fundamental strategies for the containment of SARS. However, several conditions must be met for this containment strategy to be effective.
First, the majority of the infected individuals must develop typical, identifiable clinical symptoms that can be used to distinguish between the target disease and other infections.
Second, only those with typical clinical symptoms can infect others.
Third, infected individuals are contagious only in the late stage of illness.
For SARS, these conditions were met, and quick containment was therefore possible. Most infected individuals developed severe viral pneumonia, which was distinguishable from other infections such as seasonal influenza. Furthermore, only those with severe and typical symptoms could infect others.
Finally, infected individuals were contagious only in the late stage of illness. Therefore, we were able to identify most infected individuals and isolate them as soon as they developed symptoms to prevent further transmission.
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Eventually, all chains of transmission were interrupted, and the World Health Organization (WHO) declared a global containment of SARS on Jul 5, 2003 - eight months after the emergence of the virus.
PROBLEMS WITH CONTAINMENT
In contrast, the containment strategy used for SARS has not been successful in containing this novel coronavirus.
This is because this virus does not meet the aforementioned necessary conditions. Unlike SARS, some or many infected individuals developed only mild or no symptoms, precluding the identification of all possible cases.
In Singapore, some Singaporeans who had come into contact with a group of Chinese tourists were diagnosed with the infection, despite two not having any signs of pneumonia when they first presented themselves to healthcare facilities.
In Japan, five out of the 565 evacuees from China tested positive for the virus despite not having any symptoms.
Furthermore, limited evidence suggests that infected individuals with mild or no symptoms can be contagious.
Asymptomatic infected individuals may not be a driving force for the ongoing outbreak due to a lower chance of successful transmission compared to symptomatic cases. However, if an asymptomatic individual becomes a source of the transmission chain, then contact tracing cannot be used to identify such a chain. This is a critical problem for containment.
Some accounts of transmission suggest that individuals are contagious even during the incubation period, which is the duration between exposure and the onset of symptoms.
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There is documented evidence indicating that a traveller from China passed the virus to some of her colleagues during the incubation period in Germany, which the science community is debating over.
If cases are infectious during the incubation period, it may be too late to prevent further transmission, even if we can isolate patients soon after they develop symptoms.
The majority of individuals infected with SARS did not infect any other persons. During that outbreak in Singapore in 2003, more than 80 per cent of infected individuals did not pass the virus to anyone else.
There were some “super-spreader events” in which one infected individual infected many others. These were the major amplifying factor for SARS. So far, no “super-spreading event” has been documented for the novel coronavirus, but more data is needed before we can rule out such an event.
Because possibly only a small fraction of cases are being detected and reported, it is difficult to know the exact transmissibility between individuals for this virus.
Due to the rapidly increasing number of cases in mainland China, its transmissibility is considered to be higher than that of SARS. In addition, the world of 2020 is quite different compared to that of 2003.
Many more international flights now depart from China to many more countries than before. While SARS spread to more than 30 countries and areas within eight months, the novel coronavirus has spread to more than 20 countries within one month.
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No sustained human-to-human transmission has been reported outside mainland China. However, “invisible transmission chains” may already have been established in some countries.
Therefore, we may see a sudden increase in the number of cases when such transmission chains are fully realised. This is becoming a real possibility.
SHIFT TO MITIGATION
Because containment appears less feasible and effective, we must shift our objective to mitigate the impact. Thus, the most important goal right now is to reduce the mortality rate to be as low as possible.
Every country should be prepared for an increasing number of severe cases. This may be more challenging in countries with limited healthcare resources. We urgently need to establish a mechanism to support these countries.
It is difficult to predict how the outbreak will evolve in China and other countries, but an imminent risk persists of large outbreaks outside of China. The international community should work together, and China has a critical role in this battle.
Other countries can learn from China’s current experience. For example, we must learn and distribute what measures are effective or ineffective.
The WHO should continue to play a leading role for international coordination, especially with China, to fight against this global threat.
Hitoshi Oshitani is Professor of Virology at the at the Tohoku University Graduate School of Medicine.