国立感染症研究所

81th meeting of the COVID-19 advisory boardof Ministry of Health, Labour and Welfare (April 20, 2022). Material 1

Evaluation of the latest infection status, etc.

Infection status

• With the decreasing trend mainly in metropolitan areas, the number of new cases of infection nationwide (by date of report) decreased to about 249 per 100,000 in the last week, with the ratio of this week to last week at 0.91. On the other hand, there are also regions such as Okinawa which are continuing to increase. The number of new infections by age group tends to decrease in all age groups, but it remains flat or slightly decreased in the age groups other than the 20s, where a clear decrease is observed.
• With the increasing trend in the number of new cases of infection nationwide, the number of patients being treated was still on an increasing trend, but recently began to decrease. Along with the decrease in the number of new cases of infection up to now, the numbers of severe cases and deaths are continuing to decrease.

  Effective reproduction number: On a national basis, the most recent number is above 1 (1.01 as of April 3), while the figure stands at 1.00 in the Tokyo metropolitan area and 1.01 in the Kansai area.

Local trends

* The value for new cases of infection is the number of persons per 100,000 among the total number for the latest week, based on reporting dates.

1. Hokkaido

   The number of new cases of infection is approximately 316 (approximately 364 in Sapporo City), with a ratio to the previous week of more than 1 (1.11). The individuals are mainly in their 20s or younger. The number of those in their teens or younger is particularly increasing. The use rate of beds is slightly more than 10%.

2. North Kanto

   In Ibaraki, the number of new cases of infection is approximately 242, with a ratio to the previous week of less than 1 (0.81). The individuals are mainly in their 20s or younger. It has slightly decreased or decreased in all age groups. The use rate of beds is slightly more than 10%. In Tochigi and Gunma, the numbers of new cases of infection were approximately 212 and 169, respectively, with a ratio of this week to last week of less than 1 (0.91 and 0.90). The use rates of beds are slightly less than 20% in Tochigi and approximately 30% in Gunma.

3. Tokyo metropolitan area (Tokyo and 3 neighboring prefectures)

   In Tokyo, the number of new cases of infection is approximately 318, with a ratio of this week to last week of less than 1 (0.84). The infected individuals are mainly in their 30s or younger. It has slightly decreased or decreased in almost all age groups. The use rate of beds and the use rate of beds for severe cases are both slightly more than 20%. In Saitama, Chiba, and Kanagawa, the numbers of new cases of infection are approximately 253, 234, and 269, respectively, with a ratio of this week to last week of less than 1 (0.77, 0.80, and 0.91, respectively). The use rates of beds are slightly more than 30% in Saitama, approximately 20% in Chiba and slightly more than 20% in Kanagawa.

4. Chukyo/Tokai

   In Aichi, the number of new cases of infection is approximately 218, with a ratio of this week to last week of less than 1 (0.89). The individuals are mainly in their 20s or younger. The number increased in teens or younger. The use rate of beds is slightly less than 30%. In Gifu, Shizuoka and Mie, the ratio of this week to last week was less than 1 (0.95, 0.88, and 0.92, respectively), with the number of new cases of infection at approximately 205, 158 and 220. The use rates of beds are slightly more than 30% in Gifu, slightly more than 10% in Shizuoka, and slightly more than 20% in Mie.

5. Kansai area

   In Osaka, the number of new cases of infection is approximately 274, with a ratio of this week to last week of less than 1 (0.87). The infected individuals are mainly in their 30s or younger. The number increased in those less than 10 years old. The use rate of beds is approximately 30%, and the use rate of beds for severe cases is approximately 20%. In Kyoto, Nara, and Wakayama, the numbers of new cases of infection are approximately 230, 205, and 213, respectively, with a ratio of this week to last week of less than 1 (0.93, 0.91, and 0.98). In Hyogo, the number of new cases of infection was approximately 240, with a ratio of this week to last week of 1.0. In Shiga, the number of new cases of infection is approximately 212, with a ratio of this week to last week of more than 1 (1.06). The use rates of beds are slightly less than 30% in Shiga, slightly more than 20% in Kyoto, Hyogo and Nara, and approximately 30% in Wakayama.

6. Kyushu

   In Fukuoka, the number of new cases of infection is approximately 314, with a ratio of this week to last week of less than 1 (0.93). The individuals are mainly in their 20s or younger. It tended to increase in patients less than 10 years old and patients in their 60s or older. The use rate of beds is approximately 30%. In Kumamoto, Oita, and Kagoshima, the numbers of new cases of infection are approximately 249, 222, and 283, respectively, with a ratio of this week to last week of less than 1 (0.97, 0.81, and 0.98). In Saga, Nagasaki, and Miyazaki, the numbers of new cases of infection are 418, 224, and 379, respectively, with a ratio of this week to last week of more than 1 (1.17, 1.12, and 1.08). The use rates of beds are slightly more than 30% in Saga, slightly more than 20% in Nagasaki, Oita, and Miyazaki, slightly less than 30% in Kumamoto, and slightly more than 40% in Kagoshima.

7. Okinawa

   The number of new cases of infection is the highest nationwide, at approximately 647, with a ratio of this week to last week of more than 1 (1.07). The infected individuals are mainly in their 30s or younger. Numbers in all age groups are increasing, especially those in their teens or younger and those in their 30s. Patients in their 60s or older continue to increase. The use rate of beds is slightly more than 50%.

8. Areas other than the above

   In Aomori, Iwate, Akita, Fukushima, Niigata, Yamanashi, Nagano, Okayama, Hiroshima, Yamaguchi, Kagawa, and Ehime, the numbers of new cases of infection are approximately 219, 193, 226, 210, 209, 139, 252, 239, 253, 116, 263, and 155, respectively. The use rates of beds are slightly more than 20% in Aomori, Iwate, Nagano, Okayama, and Kagawa, approximately 20% in Akita and Ehime, slightly less than 30% in Fukushima and Yamaguchi, slightly less than 20% in Niigata, slightly less than 40% in Yamanashi, and slightly more than 30% in Hiroshima. The use rate of beds for severe cases is approximately 20% in Ehime.

Future outlook and measures to be taken

• Infection status

  • In the number of new cases of infection, the moving average for the latest week has been increasing for about 3 weeks on a national basis, but is currently decreasing with a decreasing trend mainly in metropolitan areas. However, by region, in Akita, Fukushima, Niigata, Nagano, Ehime, Miyazaki and Kagoshima, the moving average for the latest week has exceeded the peak since the end of last year. Accordingly, attention should be paid to the spread of infection, by region. In addition, while there are areas such as Hokkaido, Saga and Okinawa that continue to increase, there are differences in the transition of infection status, such as decreasing trends mainly in metropolitan areas. In Okinawa, which currently has the highest level of infection in Japan, the number of infections has been increasing since the end of March.

  • The number of new infections by age group tends to decrease in all age groups, but it remains flat or slightly decreased in the age groups other than the 20s, where a clear decrease is observed. In the metropolitan area, there is generally a decreasing trend in all age groups. On the other hand, in Okinawa the number of new cases of infection continues to increase in all age groups, with the increase in teens or younger is particularly marked. In addition, the number of elderly patients continues to increase, and the infection status in the elderly should be carefully monitored in other regions.

  • The proportion of schools as the place of infection tends to increase.

  • Although the current infection status is now decreasing mainly in metropolitan areas, it continues to increase in some areas such as Hokkaido, Saga and Okinawa. It remains higher than the peak of last summer, and it is necessary to continue to watch future trends.

• Factors that increase and suppress infection

  1. The infection situation is affected by changes in factors such as the following, which increase or suppress infection. However, the increase in contact opportunities and replacement by the BA.2 lineage are thought to have a strong influence on the recent increase in the number of infected people. In addition, the decreasing trend now seen may be affected by the acquisition of immunity by vaccination, and by the efforts of citizens to avoid places and situations where the risk of infection is high.

  1. [Contact patterns]

     The nighttime population is showing an increasing trend in more than half the country. In most of the prefectures where the moving average of the number of newly infected people in the last week exceeded the peak since the end of last year, the nighttime population shows an increasing trend. Although it tended to decrease in the Tokyo metropolitan area, it has started to increase again in the last week. Movement and contact may increase toward Golden Week, and it is necessary to pay attention to the impact on the infection status.

  2. [Epidemic strain]

     It is estimated that replacement by the BA.2 lineage has progressed to about 80% nationwide, which may be a factor in the increase in the number of newly infected individuals. Overseas, replacement by the BA.2 lineage is progressing, and the number of deaths is increasing with the spread of the infection in some countries (such as the UK). Accordingly, caution is required.

  3. [Vaccinations, etc.]

     The main purpose of the third vaccination is prevention of onset and aggravation. While the third vaccination is proceeding in elderly people, the vaccination rate is still low in young people. However, it is expected that vaccination will proceed by becoming the targets for vaccination.

     It should be noted that the protective effect against the Omicron variant is lower than that against the Delta variant, and the duration is short. The infection prevention effect of the third vaccination is expected to diminish over time. In addition, the retention of immunity due to previous infections may affect trends in occurrence, by region.

  4. [Climate factors]

     As the temperature will rise day by day, it will become easier to ventilate, due to climate conditions. It is thought that a reduction of the amount of time spent indoors has a certain effect on suppressing infection; however, it should be noted that the infection spread during this period last year.

• Medical care provision system

  • In regions such as Saga and Okinawa where the number of new cases of infection continues to increase, the number of inpatient cases and the use rate of beds show increasing trends. In addition, the number of patients in home care or arranging accommodations for care is increasing in multiple regions, including Fukuoka, Saga, and Okinawa.

  • The number of cases of difficult emergency transportation was below the peak of last summer, but both suspected non-COVID-19 cases and suspected COVID-19 cases leveled off. However, the number increased in some regions.

• Efforts based on the spread of infection with the Omicron variant

  1. [Surveillance, etc.]

     It is necessary to consider effective and appropriate surveillance, in order to properly grasp trends regarding occurrences. As a system of mutant strain monitoring, genomic surveillance should be continued in order to monitor the trend regarding replacement of the BA.1 lineage with the BA.2 lineage. For severe cases, clusters, or other applicable cases, confirmation via PCR testing for mutant strains and a whole-genome analysis is required.

  2. [Efforts by local governments]
     • Local governments also need to inspect the medical care/testing system and the public health center system in order to strengthen the response based on the characteristics of the Omicron variant.
     • Based on the local infection status, it is necessary to continue to work to secure the required number of beds and medical staff, and to establish home-visit medical care and online medical care systems. It is still necessary to secure a system for prompt administration of oral therapeutic drugs and neutralizing antibody drugs, for patients with a risk of developing severe disease, such as elderly patients and patients with underlying diseases. It is also necessary to establish a system that allows treatment of the underlying disease to continue even if the patient has a novel coronavirus infection.
     • Prompt medical care support systems must be strengthened and thoroughly implemented at facilities for the elderly. When establishing a medical care support system, it is important for medical and nursing care departments to cooperate, and proceed in consultation with local concerned parties.
     • Based on administrative notices such as to prioritize health observation and improve efficiency in processing notices of the occurrence of patients, a system for outsourcing or centralization at the main office shall be secured, in order to efficiently carry out public health center operations and maintain the public health center functions required in the region. In addition, in the identification and home quarantine of close contacts, it is necessary in principle to take appropriate measures against infections according to the local infection status, and taking into account the characteristics of Omicron variant and the status of the spread of infection, it is necessary to focus on the cases of infection at facilities such as medical institutions and elderly facilities. At the same time, it is important to establish an environment where people can take a break from work or school if they feel even a little unwell.
     • In some rural areas, the number of infected people is now increasing. The above-mentioned systems need to be established in all regions.
  3. [Reinforcement of information provision to unvaccinated individuals and those receiving a third vaccination]
     • As announced on April 19, the rate of receiving a third vaccination was about 86% for the elderly aged 65 years and older, and about 49% overall. However, in order to minimize the number of severe and fatal cases, especially in the elderly, and to reduce patients with symptoms to the lowest possible level, it is necessary to steadily implement a third vaccination in the elderly and subjects under the age of 65, and to vaccinate as many desiring recipients as possible.
     • It is important for local governments to promote the provision of information on vaccination. Along with vaccination of unvaccinated individuals, a third vaccination six months or more after the initial vaccination will restore vaccine effectiveness against the Omicron variant, as well. Therefore, a third vaccination must also be steadily implemented. Vaccinated individuals have also been reported to have a lower risk of prolonged symptoms.
     • Vaccination of children from 5 to 11 years old is being implemented as a special temporary vaccination, and it is necessary to promote vaccination, considering that the obligation to make efforts does not apply to these children. In anticipation of preventing infections in children, it is also important for parents and the adults around them to be vaccinated.
  4. [Quarantine measures]

     It is necessary to verify the step-by-step review of quarantine measures, while taking into account the status of the current epidemic situation overseas and in Japan. In particular, attention should be paid to the recent epidemic status in the East Asian region. For individuals who are found to be positive by an entrance test, a whole-genome analysis should continue to be performed, to monitor the strains that are spreading overseas.

• Strengthening and thorough implementation of infection prevention measures based on the characteristics of the Omicron variant

  1. In situations and places where infection is widespread, it is necessary to strengthen and thoroughly implement infection control measures, based on the characteristics of the Omicron variant.

  • At schools, kindergartens, and day-care centers, in addition to thorough measures to prevent infections in children, it is necessary to recheck and thoroughly implement infection control measures, including the active promotion of vaccination of teachers, childcare workers, etc. It is important to establish an environment where children and workers can take a leave of absence, in the case of any poor health conditions. It is also necessary to consider securing educational opportunities through multiple measures, including staggered attendance and online lessons, and maintaining social functions. At the same time, thorough infection control measures are also required at home.
  • It is necessary to take thorough measures at nursing care facilities, in order to control infections in the elderly. Therefore, promotion of a third vaccination for residents and staff, as well as aggressive testing of staff is required. In addition, it is important to secure external support systems for infection control and medical care at facilities, and to promptly intervene when infection is confirmed at facilities.
  • At workplaces, it is necessary to utilize business continuity plans, and to reduce staff attendance at workplaces and opportunities for contact by adopting telework, promoting the taking of time off, and through other measures, so that social functions can be maintained. Thorough health management, the establishment of an environment where people can take a leave of absence, and the active promotion of occupational third vaccinations for workers are also needed

• It is essential to widely share the current infection status with citizens and business operators, and cooperate toward preventing the spread of infection.

  1. The current number of new infections continues to be higher than the peak last summer. In addition, as Golden Week approaches, it will be the season when there are more opportunities for leisure activities such as travel, events, shopping, and going out. Previously, increased contact with people who are not usually met, such as at annual events, has triggered the spread of infection. Therefore, it is necessary for citizens and businesses to cooperate to maintain the decreasing trend in the number of infections, call for thorough basic measures against infection and daily health management, to prevent a resurgence in new cases of infection.

  2. [Vaccination]

     It is important for people to receive a third vaccination as soon as possible, regardless of type, once such vaccination becomes available. People with the novel coronavirus disease may experience severe conditions even if they are young, and may also suffer from prolonged symptoms. Accordingly, it is necessary to promote vaccinations not only in the elderly, who have a risk of aggravation of symptoms, but also in younger persons, in order to protect their health.

  3. [Thorough infection control]

     Basic preventative measures are still effective against infection with the Omicron variant. Therefore, administrative officers, business operators, and citizens should continue to ensure the proper wearing of nonwoven masks, hand washing, ventilation, etc. The risk of infection becomes highest when the three Cs (crowded places, closed spaces, and close contact) overlap. However, even a single C should be avoided as much as possible, because the Omicron variant is highly transmissible.

  4. [When going out]

     Crowded or poorly ventilated places with a large number of people and loud voices, where the risk of infection is high, should be avoided. Activities with other persons should be carried out in a small group of people who usually meet each other. In principle, eating and drinking together should be done in a small group without speaking to the extent possible, and masks should be worn at all times except while eating and drinking.

  5. [Health management]

     In order to protect the lives of both ourselves and our families, and at the same time, to prevent the spread of infection with the Omicron variant, it is necessary to refrain from going out if you feel a little unwell, such as a mild fever or fatigue, and to consult with a physician and undergo tests according to local government policy. In particular, caution should be exercised when meeting persons who are at a high risk of severe illness, such as the elderly.

<< Reference: Findings on the characteristics of the Omicron variant >>

1. [Infectivity/transmissibility]

   It has been confirmed that compared to the Delta variant, the generation time has shortened to approximately 2 days (approximately 5 days for Delta). The doubling time and incubation period have also shortened, the risk of re-infection and secondary infection after infection has increased, and the speed of infection spread is very fast. According to the reported data, pre-symptomatic transmission has probably occurred to some extent as with the previous strains.

2. [Place/route of infection]

   In Japan, many cases of infection have occurred through the same opportunities as before (spending time indoors in locations with inadequate ventilation, eating and drinking, etc.), and infection is considered to have occurred via the same routes as before (droplets adhering to mucosa, aerosol inhalation, contact infection, etc.).

3. [Severity]

   It has been suggested that infection with the Omicron variant presents a lower risk of hospitalization or aggravation than the Delta variant. However, analyses to date show that the fatality due to infection with the Omicron variant is higher than that due to seasonal influenza. Although limited data suggest that the incidence of pneumonia is higher than that of seasonal influenza, this needs to be investigated through various analyses. People aged 80 years and older account for a larger proportion of deaths in this wave of the spread of the infection than during last summer. Many of these people had resided at medical or elderly facilities before they were found to be infected. It has been reported that not a few persons have died from causes other than the novel coronavirus infection itself. In particular, some have refused highly invasive treatments, while others did not meet the definition of severe disease, due to a worsening of an underlying disease, or for other reasons. Attention should also be given to a possible increase in the number of infected individuals requiring hospitalization, as test-positive persons with an underlying disease may experience disease exacerbation due to infection, and elderly infected patients may develop other symptoms, such as heart failure and aspiration pneumonia, even in the absence of COVID-19 pneumonia.

4. [Duration of viral shedding]

   Viral shedding in individuals infected with the Omicron variant decreases over time. In patients with symptoms, it has been shown that the possibility of viral shedding is low at 10 days after the date of onset. In patients with no symptoms, it has been shown that viral shedding does not occur 8 days after the date of diagnosis.

5. [Vaccine effect]

   For infection with the Omicron variant, the preventive effect of a first vaccination against disease onset is markedly reduced. Its preventive effect on hospitalization is reported to be maintained at a certain level for the first 6 months, but subsequently decreases to 50% or less. On the other hand, it has been reported overseas that a third vaccination restores the infection-preventing effect, onset-preventing effect, and hospitalization-preventing effect against Omicron variant infection, as well as how these vaccine effects are attenuated after a third vaccination. Overseas, a fourth vaccination has been started in some countries. It is necessary to collect information on efficacy and safety, and to examine the need for a fourth vaccination in Japan, and the eligible persons, starting time, etc.

6. [BA.2 lineage]

   Infection by the BA.2 lineage is spreading overseas. In Japan, both the BA.1 lineage and the BA.1.1 lineage of the Omicron variant initially entered from overseas, after which the BA.1.1 lineage became the majority strain, and is still dominant. However, the BA.2 lineage has begun to be detected at quarantine stations and other domestic facilities, and replacement with the BA.2 lineage is progressing. Therefore, this may affect the pace of the increase (decrease) in the number of cases of infection. Analyses of the effective reproduction number, risk of domestic secondary infection, and other indices have shown that the infectivity of the BA.2 lineage is higher than that of the BA.1 lineage. The generation time in the BA.2 lineage was 15% shorter than that in the BA.1 lineage, indicating that the effective reproduction number was 26% higher. In comparing the severity of the BA.1 lineage and BA.2 lineage, some animal studies suggest that the BA.2 lineage may be more pathogenic, but it has also been reported that there is no difference in the actual risk of hospitalization or aggravation. In addition, a report from the UK indicates that there is no difference in the preventive effect of vaccination, between these two lineages. In the UK, a small number of cases of reinfection with the BA.2 lineage after infection with the BA.1 lineage have been reported, and the affected patients were reported to have mainly been unvaccinated.

7. [XE lineage]

   The XE lineage of the Omicron variant is a recombinant of the BA.1 and BA.2 lineages of the Omicron variant. More than 1,500 cases have been confirmed since the first case in the UK in January. The WHO report indicated that the rate of increase in community-acquired infections was approximately 10% higher than that of the BA.2 lineage. One case of the XE lineage was identified from a sample collected on March 26 during quarantine. The National Institute of Infectious Diseases suggests that although there are no reports indicating large differences in infectivity or severity, information on the overseas infection status and findings regarding the characteristics of the virus should be collected and analyzed, as before, and genomic surveillance should be continued for purposes of monitoring.

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