Infection with the new coronavirus has reached an unprecedented scale, with the number of infected people nationwide exceeding 25,000 in mid-August in the "Fifth Wave" this summer, but since late August. , Turned around and decreased rapidly.

On the 4th, the number of infected people in Tokyo fell below 100 per day for the first time in about 11 months, and even in Japan, it fell below 1000 for 3 consecutive days until the 5th, less than 1/25 of the peak. I am.

Why did it decrease so rapidly?


At a press conference when the cancellation of the emergency declaration was decided on the 28th of last month, Shigeru Omi, chairman of the government subcommittee, said that the time when


factors leading to the spread of infection, such as consecutive holidays and Obon holidays, has passed, and the factors of expansion have passed. lost it,


▽ medical care is transmitted widely that it is now a critical state, that the sense of crisis has been shared,


▽ that the turnout of downtown at night, which is likely to spread infection has decreased,


▽ inoculation of the vaccine


It is mentioned that the

infection has decreased not only in the elderly but also in the younger generation, and that

there was an influence of the weather such as temperature and rain.

[The infection spread factor has disappeared]

It is thought that the reason for the decrease is that the period from the end of July to August, when the factors that activate the movement of people such as summer vacation, consecutive holidays, and Obon holidays are concentrated, has passed and the factors have disappeared.

[Medicine crisis transmission and infection control]

Even if infected, it was not accepted by medical institutions, and it was widely reported that medical care was in a critical situation, such as being forced to wait at home and some people dying at home. It is analyzed that the feeling has increased and the general public has become more cooperative in infection control.

[Reduced number of people at night]

Nighttime crowds in downtown areas, where infections are more likely to spread, are more frequent in Tokyo, for example, than in early July, before the fourth state of emergency was declared for over a month from mid-August to late last month. It continued to decrease by about 25% to 40%.


Furthermore, according to a trial calculation from the vaccination rate by age group, the number of unvaccinated people who were in the downtown area at night seems to have decreased by about 70% compared to the beginning of July. It may have dropped significantly to the same level as at the time of the second state of emergency.

[Effect of vaccination]

According to government data, about 30% of the total population and 80% of the elderly have completed two vaccinations, but by the middle of last month, it exceeded 50% of the total population. , It is close to 90% in the elderly.

According to data from Tokyo, the percentage of people who completed two vaccinations was as low as 18.7% in their 50s and 11.4% in their 40s as of August 10, but on the 1st of last month. 44.1% in their 50s and 31.8% in their 40s, 69.4% in their 50s and 58.9% in their 40s as of the 30th of last month, which was the deadline for declaring an emergency, 49.1% in their 30s and 31.8% in their 20s. It is 43.7% in Japan and 34.9% in 12 to 19 years old, which is increasing even in the younger generation.



In particular, since inoculation has progressed in the elderly, it is believed that the infection of the elderly at medical institutions and facilities for the elderly, which had been common in the past spread of infection, has decreased significantly.

[Effects of weather]

It has also been pointed out that it may have been affected by temperature and rain.


"There is no scientific basis yet," Omi said, but pointed out that the temperature may have dropped, making it easier to work outdoors and reducing the chances of contact in tight spaces where infections are likely to occur. increase.



It is difficult to determine which factors contributed to the reduction of infection and to what extent, and further verification will be carried out.

Infection reduction Experts' view is ...

“Vaccine + seasonal factors”

Regarding the factors behind the rapid decrease in infection, Professor Koji Wada of the International University of Health and Welfare, a member of the expert meeting of the Ministry of Health, Labor and Welfare, said, "Many people have been vaccinated, and in a cooler and air-conditioned room. I think there may be a seasonal factor that the activity has decreased and it has become easier to secure the distance between people. However, it is difficult to numerically show how much each of the multiple factors contributes to the reduction of infection. I think it's difficult. "



Regarding the outlook for future infections, he said, "If the temperature drops significantly over the coming winter, the infection may spread again. At that time, the percentage of people who have acquired immunity through vaccines or infections is relatively high. There is concern that the younger generation, who are in their late teens to 20s, will become the center of infection, and that the infection will spread to middle-aged and elderly people who have not been vaccinated, and that the infection will become more severe. There is a risk that infections will be more common in older people whose value has dropped. "



On top of that, regarding the necessary measures, "The higher the vaccination rate for winter, the more medical strain can be avoided. Those who have not been vaccinated should be vaccinated by the end of this month. On the other hand, vaccination Even if the number of infected people increases to a certain extent due to the progress of the vaccine, it is possible that medical care will not be as tight as before. It is also necessary to discuss how to grasp the new corona virus and how far to take measures. I will come. "

“Increasing proportion of people in the population who have acquired immunity”

Regarding the rapid decrease in infection, Professor Taro Yamamoto of the Institute of Tropical Medicine, Nagasaki University, who is familiar with infectious diseases, said, "It is verified how appropriate the number of infected people announced daily by the local government is compared to the actual situation. Without it, I don't think we can correctly evaluate the factors that reduce it. "



On the other hand, "I think it is certain that the proportion of people who have acquired immunity in the population is increasing due to the spread of vaccination and the increase in the number of people who have experienced infection. If we are aiming for a society that can be suppressed to a level that is humanly, socially, and economically acceptable, it is necessary to discuss what is acceptable. Evaluate the epidemic situation using the number of infected people as an index. Instead of doing so, I think we are entering a phase where the emphasis is shifting to indicators such as changes in the number of people who are seriously ill or dying. "



Furthermore, regarding the measures required in the future, "While continuing strict restrictions and measures aiming for corona zero, if the virus mutates and the infectivity changes, we may be forced into a more difficult situation than now. It is necessary to think about "coexistence with coronavirus" from the viewpoint, but from an individual's point of view, there remains a risk that oneself and one's family will be infected with the virus and become seriously ill or die. At least, it is necessary to build a treatment method and medical system that will not die. "

“Preparation for winter”

Professor Hiroshi Nishiura of Kyoto University, a member of the expert meeting of the Ministry of Health, Labor and Welfare, said, "I would like to explain the factors behind the rapid decrease in infections when the results are available during the analysis. ".



On top of that, "One thing I can say is that the" effective reproduction number ", which is an indicator of how many people are infected from one person during consecutive holidays, tends to increase, and it usually increased even during the state of emergency. There is no doubt that each person's contact behavior, such as meeting a third party who does not meet, going out and eating and drinking, will contribute to the secondary infection. Even if vaccination progresses in the future, contact will be disorderly. I'm sure there will be an outbreak when it happens. We need to prepare for the winter. "

“Increased by young people and decreased by young people”

Regarding the cause of the rapid decrease in infection, Takaji Wakita, the chairman of the expert meeting of the Ministry of Health, Labor and Welfare and the director of the National Institute of Infectious Diseases, said, "The factor is that the number of people in the downtown area at night is decreasing and vaccination is progressing. However, there is a part that cannot explain the rate of this decrease by itself. In this spread of infection, the infection that increased among the younger generation did not shift to the elderly due to the effect of the vaccine, etc. The number of infected young people has tended to increase sharply and decrease sharply even in the wave of the spread of infection so far. It is possible that it is manifesting itself as an infection situation. We have not fully elucidated how much each of the multiple factors contributes to the reduction of infection, so we would like to continue to analyze it. "



In addition, as another factor, "In the past spread of infection, there was a case that infected people remained in the downtown area of ​​the city even if it turned to a decreasing phase, but this time it is due to the influence of vaccination, or clusters in the downtown area as well. The number of clusters is decreasing, and there are reports that the number of clusters occurring in facilities for the elderly is decreasing and the size of clusters is getting smaller even if a breakthrough infection occurs. "



On the other hand, regarding whether the virus is changing, "We are analyzing the genome of the new coronavirus from time to time, but there is a big change in the virus itself compared to the current data when the infection was rapidly increasing and the rapid decrease is seen. I don't think there is any. I suspect that the virus itself is attenuated at this point. "



On top of that, regarding the measures that will be required in the future, "In some areas, infections by foreigners who have difficulty receiving vaccines are becoming conspicuous. It is very important to take measures to deliver it. "