Experts explain Japan's rapid decline in new cases Experts explain Japan's rapid decline in new cases
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Experts explain Japan's rapid decline in new cases

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    Experts analyze sudden shift

    During Japan's fifth coronavirus wave this summer, daily cases rose to unprecedented levels – surpassing 25,000 in mid-August. But by the end of the month, infections started plunging.

    As of October 19, the daily tally had remained below 500 for three straight days. That's less than a 50th of when the virus was at its most rampant.

    The government lifted a state of emergency and other intensive measures in all targeted prefectures on September 30.

    Graph: COVID-19 Daily Cases in Japan

    The precise reasons for the rapid improvement are yet to be established and analysis is ongoing. Here is what some experts said:

    Omi Shigeru, head of the government's advisory panel on the pandemic

    Omi gave several reasons for ending the emergency measures at a news conference on September 28.

    • Long weekends and holidays that could have triggered a spike have passed.
    • People changed their behavior and took a stricter approach to anti-infection measures when they saw how hospitals were overwhelmed and heard reports of infected people dying at home.
    • Fewer people were visiting downtown areas at night.
    • The nationwide vaccination rollout has progressed, bringing down the number of new cases not only among the elderly but also younger people.
    • Weather conditions deemed to be a risk factor have changed.

    Omi suggested that people tend to spend more time outdoors in milder weather, which reduces close contact in small spaces where infections are more likely to spread. At the same time, he said this cannot be scientifically verified, and that he will continue to examine factors that contributed to the rapid decline.

    Professor Wada Koji, International University of Health and Welfare

    Wada is a member of the health ministry's expert panel on the coronavirus. He too says the decline could partly be due to the vaccination rollout and seasonal factors. He was referring to lower temperatures, which prompt people to spend more time away from air-conditioned, indoor spaces.

    Wada says it is difficult to quantify exactly what has contributed to the decline. He warns that cases could increase again as temperatures fall, adding that it would likely happen first among people in their late teens and 20s. That is because a smaller portion of people in those age groups have gained immunity through infection or vaccination. Wada says the virus would likely then spread among unvaccinated middle-aged and elderly people, who could become seriously ill. He also points out that antibody levels in vaccinated elderly people will have declined due to the time that has passed since they received their shots.

    As for the medical situation, Wada says a higher vaccination rate will likely prevent hospitals from being overwhelmed. He hopes unvaccinated people get their shots by the end of October.

    Professor Yamamoto Taro, Nagasaki University's Institute of Tropical Medicine

    Yamamoto says he can't assess the factors behind the rapid decline without examining the accuracy of the daily case numbers reported by Japan's municipalities.

    At the same time, he points out that more people have acquired immunity through vaccination or infection. He says the virus could become a part of our daily lives if we aim for a society in which the resultant illness is acceptable to a certain degree. He's calling for discussions to determine tolerable levels from a human, social and economic perspective.

    Yamamoto believes Japan is entering a new phase in which the severity of the situation is not determined by case numbers, but by the number of seriously ill patients and deaths. He also warns that the virus could mutate and become even more transmissible.

    Yamamoto says methods of treatment and improvements to the healthcare system must be established as a safety net to prevent fatalities and bolster services for the seriously ill.

    Professor Nishiura Hiroshi, Kyoto University

    Nishiura is also a member of the health ministry's expert panel on the coronavirus. He too is looking for scientifically based explanations about what's caused the rapid fall in cases.

    He says one thing is certain: the reproduction rate of the virus, which indicates the average number of people one person will infect, tends to rise after holidays and long weekends when people travel, meet others and dine out more.

    Nishiura says an unregulated increase in person-to-person contact will certainly result in another wave of infections, regardless of the vaccine rollout. He's calling for preparations in case of a winter outbreak.

    This article was published on October 21, 2021.

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