国立感染症研究所

83th meeting of the COVID-19 advisory boardof Ministry of Health, Labour and Welfare (May 11, 2022). Material 1

Evaluation of the latest infection status, etc.

Infection status

• The number of new cases of infection nationwide (by date of report) continued to decrease to roughly 175 per 100,000 persons in the last week, with a ratio of numbers for this week to last week of 0.98. However, in addition to the influence of the Golden Week holidays (GW) on tests and medical care, the movement of people during GW and the situation in which the virus has nearly been replaced by the BA.2 lineage may have affected the trend, and it is therefore necessary to monitor future movements.
• The number of new cases of infection by age group increased for persons in their 20s, but remained flat or decreased in other age groups.
• Along with the decrease in the number of new cases of infection nationwide, the numbers of patients receiving treatment, severe cases, and deaths also continued to decrease.

  Effective reproduction number: On a national basis, the most recent number is below 1, at 0.94 (as of April 24). The figure stands at 0.90 in the Tokyo metropolitan area and 0.94 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 302 (roughly 313 in Sapporo City), with a ratio of numbers for this week to last week of less than 1 (0.92). The individuals are mainly in their 20s or younger. In particular, the increase among those in their 20s is marked. The use rate of beds is slightly less than 20%.

2. North Kanto

   In Ibaraki, the number of new cases of infection is approximately 121, with a ratio of numbers for this week to last week of less than 1 (0.83). The individuals are mainly in their 20s or younger. In particular, the increase among those in their 20s is marked. The use rate of beds is slightly more than 10%. In Tochigi and Gunma, the numbers of new cases of infection are approximately 134 and 132, respectively, with a ratio of numbers for this week to last week of less than 1 (0.83 and 0.94). The use rate of beds is slightly more than 10% in Tochigi and slightly less than 30% in Gunma.

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

   In Tokyo, the number of new cases of infection is approximately 171, with a ratio of this week to last week of less than 1 (0.88). The infected individuals are mainly in their 30s or younger. The number has decreased slightly or decreased in all age groups. The use rate of beds and the use rate of beds for severe cases are both slightly more than 10%. In Saitama, Chiba, and Kanagawa, the numbers of new cases of infection are approximately 132, 105, and 127, respectively, with a ratio of this week to last week of less than 1 (0.85, 0.78, and 0.82, respectively). The use rates of beds are slightly more than 20% in Saitama, slightly more than 10% in Chiba, and slightly less than 20% in Kanagawa.

4. Chukyo/Tokai

   In Aichi, the number of new cases of infection is approximately 162, with a ratio of this week to last week of more than 1 (1.02). The individuals are mainly in their 20s or younger. The number is increasing in those in their 20s, and decreasing in other age groups. The use rate of beds is slightly more than 20%. In Gifu and Shizuoka, the numbers of new cases of infection are approximately 163 and 126, respectively, with a ratio of this week to last week of more than 1 (1.09 and 1.15, respectively). In Mie, the number of new cases of infection is approximately 136, with a ratio of this week to last week of less than 1 (0.98). The use rates of beds are slightly less than 20% in Gifu, and slightly more than 10% in Shizuoka and Mie.

5. Kansai area

   In Osaka, the number of new cases of infection is approximately 198, with a ratio of this week to last week of more than 1 (1.03). The individuals are mainly in their 20s or younger. The number is increasing in those in their 20s, and decreasing in other age groups. The use rate of beds is slightly less than 20%. In Nara and Wakayama, the numbers of new cases of infection are 128 and 158, respectively, with a ratio of this week to last week of more than 1 (1.09 and 1.06). In Shiga, Kyoto, and Hyogo, the numbers of new cases of infection are 146, 188, and 158, respectively, with a ratio of this week to last week of less than 1 (0.99, 0.97, and 0.98). The use rates of beds are approximately 20% in Shiga and Hyogo, slightly less than 20% in Kyoto, slightly more than 10% in Nara, and slightly more than 20% in Wakayama.

6. Kyushu

   In Fukuoka, the number of new cases of infection is approximately 251, with a ratio of this week to last week of less than 1 (0.96). The individuals are mainly in their 20s or younger. The number is increasing in those in their 20s and slightly increasing in those in their 60s, and decreasing slightly or decreasing in other age groups. The use rate of beds is approximately 20%. In Nagasaki, Kumamoto, and Oita, the numbers of new cases of infection are approximately 213, 191, and 212, respectively, with a ratio of this week to last week of less than 1 (0.90, 0.99, and 0.98). In Saga, the number of new cases of infection is approximately 263, with a ratio of this week to last week of 1.0. In Miyazaki and Kagoshima, the numbers of new cases of infection are approximately 250 and 281, respectively, with a ratio of this week to last week of more than 1 (1.05 and 1.01). The use rates of beds are slightly more than 20% in Saga, Nagasaki, and Kagoshima, approximately 20% in Kumamoto and Oita, and slightly less than 20% in Miyazaki. The use rate of beds for severe cases is approximately 20% in Miyazaki.

7. Okinawa

   The number of new cases of infection is the highest nationwide, at approximately 797, with a ratio of this week to last week of more than 1 (1.19). The individuals are mainly in their 20s or younger. Numbers in all age groups are increasing; however, those in their 10s to 20s have increased particularly markedly. The use rate of beds is slightly more than 40%. The use rate of beds for severe cases is slightly more than 20%.

8. Areas other than the above

   In Aomori, Iwate, Akita, Fukushima, Ishikawa, Nagano, Hiroshima, Kagawa, and Kochi, the numbers of new cases of infection are approximately 174, 146, 175, 166, 228, 121, 232, 224, and 209, respectively. The use rates of beds are approximately 20% in Aomori, Kagawa, and Kochi, and slightly more than 20% in Iwate, Akita, Fukushima, Ishikawa, Nagano, and Hiroshima.

Future outlook and measures to be taken

• Infection status

  • It should be noted that it is difficult to accurately evaluate the infection status at this point, because the number of examinations and tests was small during GW.

  • As for the number of new cases of infection nationwide, the number has continued to decrease in large cities, mainly in the Tokyo metropolitan area. On the other hand, in other regions, it has been increasing and decreasing repeatedly. Furthermore, in Okinawa, there is a difference in the time course of the infection status, as the number of cases continues to increase with a plateau period. By region, the moving average for the last week is lower than the peak of last summer in the Tokyo metropolitan area, etc. In contrast, the moving average for the last week is higher than the peak from the end of last year in Okinawa and Kagoshima.

  • Also, although it is not the moving average for one week, it is necessary to keep in mind that when comparing the nationwide infection status for the last 3 days (Sunday to Tuesday) with the same days of a week 2 weeks prior containing consecutive holidays, there is a tendency for an increase in infection. In addition, it is also necessary to assume that the number of reports will increase in the weeks following a period of consecutive holidays, due to the influence of increased opportunities for contact at travel destinations, as well as an increased probability of infection due to an increase in the nighttime population.

  • The number of new cases of infection by age group increased in persons in their 20s, but remained flat or decreased in other age groups. In the Tokyo metropolitan area, the number has remained flat or decreased in all age groups, while in several local cities such as Okinawa and Miyazaki, an increase among persons in their 20s has been observed. In Okinawa, the number of new cases of infection is increasing in all age groups. Especially, the number in teens has increased markedly, and the number in the elderly is continuing to increase.

  • As for the place of infection for new cases, the proportion of places that serve food and drink among those in their 20s is approximately 6%, showing an increasing trend (approximately 2% in all ages). It is necessary to pay attention to whether the increase in this age group will lead to a future spread of the infection, and also to give attention to the infection status in the elderly and effects on medical care.

  • As for the future infection situation, it may be affected by factors that increase infections, such as active movements of people during GW and the ongoing substantial replacement by the BA.2 lineage, as well as factors that suppress infection, such as a third vaccination, etc. Therefore, it is necessary to continue to monitor future trends.

• Factors that increase and suppress infection

  1. The infection status is affected by the following factors, which increase or suppress infection. However, it will be necessary to continue to pay close attention to the infection status, for some time in the future.

  1. [Contact patterns]

     While the nighttime population has decreased mainly in metropolitan areas, the number increased sharply after the peak time at the end of last year in some rural cities. In addition, it is necessary to pay attention to the influence on the future infection status due to active movement of people and an increase in opportunities for contact during GW.

  2. [Epidemic strain]

     The replacement by the BA.2 lineage has generally progressed, which may be a factor in the increase in the number of newly infected individuals and the slowdown in the decrease. Overseas, replacement by the BA.2 lineage is progressing, and the number of deaths has also increased with the spread of the infection in some countries (such as the UK). Accordingly, caution is required.

  3. [Vaccinations, etc.]

     The main purpose of a third vaccination is prevention of onset and aggravation. While the third vaccination is proceeding in the elderly and also in young people, it is expected that the vaccination rate will further improve as young people become targets of 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. However, elevated temperatures and rainfall may increase indoor activities.

• Medical care provision system

  • In Okinawa, the number of inpatients, the use rate of beds, and the use rate of beds for severe cases have been increasing during GW. On the other hand, in other regions, the use rate of beds and the numbers of home care recipients and medical treatment adjustments have decreased, with the exception of some areas.

  • As for cases of difficult emergency transportation, the national total is lower than the peak in the summer of last year, but has shown a slight increasing trend after the decline stopped. There has been a slight increase in the number of suspected non-COVID-19 cases. In some regions, the number of suspected non-COVID-19 cases has been increasing with an increase in the number of infected patients, showing regional differences.

• 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. In addition, it is necessary to continue monitoring the trends of variants through genomic surveillance. For severe cases, clusters, and 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 deaths that occurred at home after January of this year, approximately 80% of the patients have been aged 70 years and older, which is similar to the trend of all deaths during the same period, suggesting that many patients die from factors other than the novel coronavirus. The vaccination rate in these fatal cases was confirmed to be a certain number of those who had completed the second vaccination, due to the progress of vaccination in Japan. Local governments are trying to speed up efforts to make contact with infected persons who are at a high risk of becoming severely ill, and it is important to continue to make efforts to provide the necessary medical care to home care recipients.
  3. [Reinforcement of information provision to unvaccinated individuals and those receiving a third vaccination, etc.]
     • As of May 10, the rate of third vaccinations was roughly 88% for the elderly aged 65 years and older, and roughly 55% overall. Vaccination of elderly persons is expected to reduce the risk of severe illness and death. In order to minimize the number of severe and fatal cases, and to reduce the number of patients with symptoms to the lowest possible level, it is necessary to steadily implement a third vaccination in subjects, and to vaccinate as many desiring recipients as possible. As for a fourth vaccination, it is necessary to provide appropriate guidance on vaccination based on the fact that it will be implemented from the end of May as a special temporary vaccination for persons aged 60 years or older, persons with underlying diseases at high risk of severe symptoms, and other persons deemed by doctors to be at a high risk of severe symptoms, in order to prevent such symptoms.
     • 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.

  • In schools, kindergartens, nursery schools, etc., it is necessary to make efforts to continue educational activities as much as possible, after reconfirming and thoroughly implementing infection control measures, including active promotion of vaccinations for teachers and nursery teachers, as well as thorough implementation of infection control measures for children, while sharing situations where the risk of infection in children and students increases with staff, children, parents, 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 the infection.

  1. Although the number of new cases of infection is decreasing nationwide, the current number of new infections continues to be higher than the peak last summer. Therefore, it is necessary for citizens and businesses to cooperate to maintain the decreasing trend in the number of infections, and to call for thorough basic measures against infection and daily health management, in order to prevent a resurgence in the number of 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 infection by the Omicron variant, as well as information regarding how these vaccine effects are attenuated after a third vaccination.

6. [BA.2 lineage]

   Overseas, the number of infected patients has increased, while replacement with the BA.2 lineage is progressing. However, the number is currently decreasing worldwide. In Japan, the influx of the Omicron variant from overseas initially comprised both BA.1 and BA.1.1; however, BA.1.1 has since become dominant. Currently, 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, BA.4, BA.5, and BA.2.12.1 lineages]

   The XE lineage of the Omicron variant is a recombinant of the BA.1 and BA.2 lineages of the Omicron variant. Two cases of the XE lineage were identified from a sample collected in quarantine. The WHO report indicated that the rate of increase in community-acquired infections was approximately 10% higher than that of the BA.2 lineage. In some countries and regions, the detection rates of the BA.4, BA.5, and BA.2.12 1 lineages have increased, and the BA.2 lineage has been replaced by these variants, suggesting its superiority in terms of an increase in the number of infected patients. The National Institute of Infectious Diseases has suggested 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)