Suppressing the novel coronavirus: superspreader-oriented approach deployed in Japan

This is a journalistic writing, not a experts article.

Early alerts in Asia

Since the outbreak of the novel coronavirus in Wuhan, Asian countries that have been hit by SARS have implemented a countermeasure quickly. China locked the city down and demanded strong social distancing in all around the mainland. Hong Kong, Taiwan, Singapore and Vietnam quickly closed border with China. South Korea has prepared to carry out a large number of tests. All eastern Asian countries started strict tracking of an infected patient.

Japan’s initial response to the virus was relatively slower than the other neighboring countries. Border control for Chinese people was less strict than for other countries. Accommodation for quarantine was scarce. In any case, however, preventive measures against infection were strongly recommend to the people since late January. People washed their hands and facility maintainers increased the frequency of disinfection. Companies have encouraged their workers to work from home. Many mass-gathering events have been canceled.

Asian countries are struggling, but slowing down the spread of the novel coronavirus.

Europe: it's too late

Confirmed cases of the novel coronavirus have increased rapidly in Europe. But researchers believe the virus has been growing for a long time. They estimate that the virus arrived in Europe in mid-January, the same as in Asia. Unfortunately European countries were unaware of it for a month and had taken no action, in contrast to Asian countries.

[translation] "It started from someone infected in Germany probably around the 24th, 25 or 26th of January and then came to that area [northern Italia] where he sowed the infection"
"Completely unknowingly either because it was completely asymptomatic or because he mistook the symptoms of Covid-19 for those of a normal flu"
――Massimo Galli, infectiousologist at Sacco Hospital in Milan. (Interview on a Italian newspaper)
[translation] "This virus has probably been circulating in Italy since mid-January"
――Christian Drosten, German virologist. (Interview on a German radio)

In the Europe, a rapid increase in the number of confirmed cases is not really indicative of current rate of infections, but rather a situation that is tracking the virus that have already spread. Continental Europe has no control over the virus because the full extent of the epidemic is still not known.

Test-and-isolate approach is not enough, prevention is needed

Epidemic data suggest that the novel coronavirus has a long incubation period and a number of COVID-19 cases are asymptomatic. In the extreme case, the result of the test for a person fluctuated. In other words, sometimes result of the test is positive and sometimes negative for a same person [e.g. this story]. Japanese doctors were aware of that tendency from analysis of Diamond-Princess cruise ship cases.

This tendency suggests that test-and-isolate approach is not enough to contain the novel coronavirus. Asymptomatic cases easily get past the checkpoint of tests and spreads the infection outside of authorities' eyesight. [NOTE: This does not mean test-and-isolate strategy is not effective. Isolation is still important.]

Prevention of infection ‒washing hands, sterilization, social distancing, etc.. ‒ is relatively important for containing the novel coronavirus. At least in Asian countries, sterilization for shared tool is strongly recommended (e.g. Janitors sterilize door knobs frequently).

Moreover, some Asian countries chose wider extent of isolation. For example, China locked down whole city of Wuhan. Singapore has isolated persons who had close contacts to patients, regardless of test results of themselves. The number of isolated people is 10-100 times the number of infected people.

Finding possible superspreaders

In the past outbreak of coronavirus (SARS), it was reported that a small number of patients caused a large number of infections. Those distinguishable patients are called as 'superspreaders'. Grantz, Metcalf & Lessler (15th Feb 2020) have pointed out that novel coronavirus is possibly transmitted by a few superspreaders. If it's possible to find super spreader before they transmit virus to others, it's possible to suppress the spread of the epidemic. But how can we do it?

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Dr. Hiroshi Nishiura, a professor of Hokkaido University, and his colleague had tried to examine the possibility. Finally, they found that the variance in number of virus transmission from each patient is large: most of infection is caused by a few superspreaders.

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Analysis of coronavirus transmittion by the government team. Most of transmission is caused by few sperspreaders.About 80 percent of patients did not transmitted the virus to others.

Moreover, he and his colleague have tried to identify common conditions among superspreading events. In late February, the government's team announced environmental condition is the key for occurrence of superspreading events:

1. People are packed in close distance (persons can touch each other).
2. Ventilation of the room is insufficient.
3. People are frequently talking, shouting or singing.
[NOTE: These analysis will be updated]

The government advised people to avoid places that meet these conditions (in addition to former advice to avoid contact and droplet infection). Their forecast was confirmed in early March. Superspreading events occurred in four nightclubs was detected by Osaka public health authority. Nightclubs meet all three conditions in the advice of the government team.

The government team will continue tracking patient clusters to find superspreading events. Identifying events helps to find hidden patients and aids the isolation approach. Insights from the analysis of the events will be fed back into the prevention policy.

The outcome of the government's advice is currently under review. We have to wait for evidence. But at least no superspreading event was detected in the last two weeks, even though the future is unknown.

Superspreader-oriented approach is required until preparation of vaccine

Lockdown (or strong social distancing) is very effective at suppressing infection. However, it is difficult to determine when and how much to ease the social distancing. Today, China worries about the second wave of the infection.

The Superspreader-oriented approach is one of the answers. That approach demands minimum lockdown of spaces which is meeting several conditions. In Tokyo, most of the people keep their usual lifestyles. We must continue suppression on the novel coronavirus until the preparation of vaccine. Minimum changes in our lifestyle brought by the new approach help long-term suppression of the novel coronavirus.

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