国立感染症研究所

35th meeting of the COVID-19 advisory board of Ministry of Health, Labour and Welfare (May 19, 2021).  Material 1

 

Evaluation of the latest infection status, etc.

Infection status

  • The number of new cases of infection nationwide has stopped increasing based on the reporting date, and the number in the most recent week is approximately 32 per 100,000 population. As in the previous week, the figure does not indicate nationwide spread of infection, and the trends are different between regions; some are in an increasing trend, some remains the same, and some are in a decreasing trend. The numbers of severe patients and deaths are continuing to increase.
  • The number of infections has not clearly decreased at present. The effects of the movement of people during GW and the effects of mutant strains are intricately intertwined with the effects of various measures to control the infection, and it is difficult to evaluate the statuses and estimate the future. Attention should be paid to future movements.

    The nationwide effective reproduction number remains stable around 1, most recently 1.01 (as of May 2).

Analysis of infection status [local trends]

 *The value of new cases of infections is the number of people per 100,000 in the total number for the latest week on the basis of reporting dates. The effective reproduction number represents the mean value of the most recent week (as of May 3)

  1. (1) Kansai area
    • In Osaka, 6 weeks have passed since the start of priority measures, such as for prevention of the spread of disease (hereinafter referred to as “priority measures”), and 3 weeks since the start of emergency measures. The ratio of this week to last week has been 1 or lower for the most recent 2 weeks and the number of new cases of infection is decreasing, but remains extremely high. The nighttime and daytime populations rapidly decreased to the previous lowest level, and then increased. It took approximately 5 weeks from the decrease in the de facto population to the resulting decrease in the number of new cases of infection. The effective reproduction number is 0.87, 0.99, and 0.98 in Osaka, Hyogo, and Kyoto, respectively. While the number of new cases of infection is expected to continue to decrease, careful monitoring is necessary including the de facto population.
    • The number of new cases of infection is about 51, 36, 37 and 34 in Osaka, Hyogo, Kyoto and Nara, respectively. A decreasing trend has been generally observed, except for Kyoto whose figure is almost flat, but the number of new cases of infection is high in all age groups.
    • Mainly in Osaka and Hyogo, the medical care provision systems and public health systems are under very severe pressure. General medical care has been inevitably restricted. Efforts have been made to secure beds. It is essential to keep a downward trend in the number of new cases of infection to protect the system for necessary and timely care.
    • In Wakayama, the number of new cases of infection is in a decreasing trend, about 12. The figure remains almost stable, about 23, in Shiga.
  2. (2) Metropolitan area (Tokyo and its 3 neighboring prefectures)  
    • In Tokyo, 5 weeks and 3 weeks have passed since the start of priority measures and emergency measures, respectively. In Saitama, Chiba and Kanagawa, 4 weeks have passed since the start of priority measures. The number of new cases of infection remains almost stable in Tokyo (though the status is difficult to assess), and it remains stable or slightly increased in Saitama, Chiba and Kanagawa; the figure is about 38, 22, 16 and 22, respectively in these prefectures. Many people are in their 20s to 50s. The ratio of this week to last week increased after GW and is generally in a decreasing trend most recently.
    • In Tokyo, the nighttime and daytime populations reached a level 25% lower than the lowest value during the second Declaration, showed an increasing trend after GW, and then has become the same level of the lowest during the second Declaration. Three weeks have passed since the decrease in nighttime population was observed, but the number of new cases of infection has not been past the peak. The nighttime population remains stable or is increasing after GW also in Saitama, Chiba and Kanagawa, and the daytime population increased in Chiba and Saitama. The effective reproduction number is 1.03, 1.57, 1.08 and 1.14, respectively, and the number of cases of infection may increase or decrease. It is necessary to carefully follow movements in the de facto population and the number of new cases of infection.
  3. (3) Chukyo area
    • In Aichi, 4 weeks and 1 week have passed since the start of priority measures and emergency measures, respectively. The trend of rapid increase in the number of new cases of infection is continuing and the figure has reached about 52. The ratio of this week to last week has remained 1 or higher over about 8 weeks since late March. The cases of infection are mainly of those in their 20s to 30s, but the number of new cases of infection tends to increase in almost all generations. The burden on medical institutions and public health centers is increasing, the use rates of beds are at high levels, and the medical care provision systems are under severe pressure.
    • The nighttime population remains stable after issuance of the Declaration of State of Emergency, and has fluctuated around the lowest level during the second Declaration of Emergency State. In contrast, the daytime population started to increase from the latter half of GW and slightly decreased after issuance of the Declaration of State of Emergency. More than 4 weeks have passed since a decrease in the de facto population was observed, but the effective reproduction number has been 1 or higher, and the number of new cases of infection may continue to increase.
    • One week has passed since the start of priority measures in Gifu and Mie. The trend of increase in the number of new cases of infection is continuing in Gifu with the figure reaching about 44. Although the nighttime and daytime populations are decreasing, it is necessary to watch carefully whether the number of new cases of infection will decrease. The figure remains stable, about 18, in Mie. The ratio of this week to last week has rapidly increased since mid-May in Shizuoka and has been 1 or higher for about 3 weeks. The number of new cases of infection is about 17, and should receive close attention.
  4. (4) Kyushu/Okinawa
    • One week has passed since the start of emergency measures in Fukuoka. The number of new cases of infection has rapidly increased mainly in persons in their 20s and 30s since mid-April. The rate of increase slightly slowed down most recently, but the number is still very high, about 64. The ratio of this week to last week has remained 1 or higher over 6 weeks since early April. The bed occupancy rate is rapidly increasing and the burden on the medical care provision systems is still large.
    • The nighttime population was decreasing but did not reach the lowest level during the second Declaration of State of Emergency; it has remained stable after issuance of the Declaration of State of Emergency, and the daytime population increased before issuance of the Declaration of State of Emergency but slightly decreased afterwards. The effective reproduction number has remained 1 or higher, and the number of new cases of infection may continue to increase.
    • Priority measures have been taken since May 16 in Kumamoto. The number of new cases of infection had rapidly increased; the rate of increase slowed down most recently, but the figure is high, about 39.
    • A turn to decline has been observed in other prefectures in the Kyushu area, but the figures are still high, about 29 and 38 in Saga and Oita, respectively. The effective reproduction number is 1.35 in both prefectures; the ratio of this week to last week is in a decreasing trend which may continue and should be carefully monitored.
    • In Okinawa, 5 weeks have passed since the start of priority measures. Despite the priority measures, the number of new cases of infection has increased since GW, mainly in the working generations, 20s and 30s, in the metropolitan areas including Naha City and the Yaeyama area, with figures as high as about 57. There have been infections in persons coming from outside the prefecture. Medical care is expected to be in an impending situation if the number of cases of infection increases. There is particular concern that transmission of infection in the elderly could cause an increase of severe patients.
  5. (5) Other areas under emergency measures (Hokkaido, Okayama and Hiroshima)
    • In Hokkaido, priority measures and emergency measures were applied on May 9 and May 16, respectively. Rapid increase in the number of new cases of infection is continuing; the figure is very high, about 72. The ratio of this week to last week has been 1 or higher for about 6 weeks. The figure is at a high level, about 125, in Sapporo City, and many cases with an unknown link have occurred in the community. Clusters also occurred at hospitals and welfare facilities. The effective reproduction number is high, 1.57, and may continue to increase. The medical care provision systems in Sapporo have been under severe pressure, the use rate of beds is at a high level, and there have been cases of wide-area medical evacuations transported outside the city.
    • Emergency measures were applied to Okayama and Hiroshima on May 16. The figures are high, about 59 and 53, respectively. The ratio of this week to last week has been 1 or higher for 7 weeks in Okayama, and 5 weeks in Hiroshima. The use rate of beds is at a high level in both prefectures. In Okayama, the nighttime and daytime populations are decreasing. The effective reproduction numbers are high, i.e., 1.30 and 1.76, respectively. The infection may further spread from now on.
  6. (6) Other areas under priority measures, such as for prevention of the spread of disease (Gunma, Ishikawa, and Ehime)
    • Priority measures have been implemented since May 16 in Gunma and Ishikawa. The number of infections have been in a decreasing trend from mid-May in Gunma, and it stopped increasing most recently in Ishikawa; the figures are about 24 and 29, respectively. The effective reproduction number is 1 or higher in both prefectures, and it is necessary to carefully monitor the changes in the number of cases of infection.
    • In Ehime, 3 weeks have passed since the start of priority measures. The number of new cases of infection has decreased since late April, reaching approximately 6.
  7. (7) Areas other than those listed above
    • The number of new cases of infection in Fukushima, Ibaraki, Yamaguchi and Kagawa exceeded 15, i.e., about 17, 16, 25 and 21 , respectively. A decreasing trend has been observed in Fukushima and Kagawa, and an increasing trend in Ibaraki. The effective reproduction number is 1 or higher, including Yamaguchi, and the situation should be carefully monitored.

Analysis of mutant strains

  • The proportion of the mutant strain first detected in the UK (B1.1.7) became about 80% in national total in screening test, suggesting that the existing strains were almost all replaced by the mutant strains, except for some regions. In addition, analysis of screening at private testing institutions by the National Institute of Infectious Diseases also demonstrates that the existing strains have already been replaced by the mutant strains in many regions.
  • It is necessary to establish medical care systems and provide treatments assuming the possibility of increased risk of disease becoming severer due to B.1.1.7.
  • In addition, it has been reported that B.1.617 (mutant strain detected first in India) is being replaced with the existing ones overseas, and it has been suggested that this strain may be more infectious than B.1.1.7. Therefore, it is necessary to continue analyses.

Measures to be taken

  • In some areas designated to be controlled under emergency measures and those under priority measures such as for prevention of the spread of disease, the number of infections seem to decrease or stop increasing owing to cooperation of citizens and business operators. On the other hand, there are some regions where the number of infections has not clearly decreased. In the spread of infection mainly of mutant strain (VOC) this time, it takes a longer time before a decrease in the flow of people results in a decrease in the number of new cases of infection. Currently, the effective reproduction number has not decreased to much lower than 1 with the previous efforts. It is required to discuss necessary measures based on the infection status and the high infectivity of mutant strains and to implement them in a timely manner.
  • In other regions, if the number of new cases of infection is at a high level and then increases/remains, the speed of infection will increase more than before and the burden on medical care provision systems will become larger. Therefore, necessary actions should be promptly taken.
  • It is crucial to proceed with measures in the early stages of the epidemic. Each local government is required to conduct measures promptly to establish a meeting structure to utilize advice of experts on public health and infectious diseases for countermeasures and to act from an early stage and establish a cooperative system to secure medical care provision systems based on future prospects by using various data, including the flow of people.
  • While it is estimated that the existing strains have been replaced with B.1.1.7 as the predominant strains in most regions with some exceptions, it is necessary to take measures focusing on understanding the actual situation using virus genomic surveillance in order to reinforce the measures against new mutant strains. Particularly for B.1.617, which has been positioned as VOC, it is essential to suppress the spread of infection in Japan as much as possible by following measures: nationwide monitoring through genomic surveillance, and active epidemiological surveys. In addition, the border control measures against infection from India, Pakistan, and Nepal have been strengthened. Prompt action will be required based on the occurrence status in other countries and quarantine.
  • In addition to the effect of vaccines to prevent onset of the disease, there have been reports suggesting effectiveness in the prevention of aggravation and infection. It is expected that vaccinations in wider populations can reduce severe cases and then inhibit infection of the virus. Vaccinations in the elderly has begun. It is expected that the vaccination both residents and workers in elderly facilities, etc. can suppress clusters. It is necessary for the national and local governments, with the cooperation of local medical associations, to work together to offer vaccinations for many people as quickly and efficiently as possible.

Figures (Number of new infections reported etc.) (PDF)

Copyright 1998 National Institute of Infectious Diseases, Japan

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