The sixth wave of the spread of the infection seems to have exceeded its peak and has finally entered a declining phase.



However, while the rate of decline is slower than it was when it increased, the number of deaths is increasing at an unprecedented pace.



What are the symptoms and sequelae of the Omicron strain?



And the spread of infection of the different strains of Omicron strain "BA.2".



I have summarized what I have learned.



(As of February 25, 2022)

“Peak out” also slows down

In mid-February, the number of new coronavirus infections began to decline nationwide for the first time in two and a half months, and is in a declining phase in many regions.



In the sixth wave of the spread of the Omicron strain, the number of infected people has already exceeded 3 million in 2022 alone, but it seems that it has finally "peaked out".



However, the rate of decrease is gradual, and the number of newly infected people in the week is 0.88 times that in the previous week until February 24th.

An expert meeting of the Ministry of Health, Labor and Welfare said on February 24, "Although it is on a downward trend, its speed is slowing down, unlike the situation in the summer of 2021, which continued to decline with the acceleration of vaccination. There is a possibility that it will start to increase again nationwide. "



Looking at the trend of overseas infections that spread before Japan, in the United Kingdom, the number of newly infected people in a week exceeded 1 million around January 10, and then decreased by about 40% at a stretch.



Although it leveled off for about two weeks from mid-January, it has decreased again to more than 270,000 in the week until February 24th.

In the United States, according to the CDC = Centers for Disease Control and Prevention, the number of newly infected people per day exceeded 1.3 million on January 10, and after an average of 800,000 per week, it gradually decreased, and it gradually decreased on February 23. As of the day, the average number of people per week is about 75,000.



Overseas, the inoculation rate of booster vaccination is 55.8% in the United Kingdom and 28.1% in the United States, and the scale of infection spread is larger than in Japan, and the number of people with immunity is increasing, so infection is rapidly occurring. It is believed that this is in the background of the decrease.


(Data is Our World in Data as of February 22)

Number of deaths exceeds the 5th wave

Under these circumstances, the number of people dying in Japan continues to be the highest ever.



The number of deaths reported on the 1st was 34 on January 26, 2022, about a month ago, but after exceeding 103 and 100 on February 4, 2 On the 22nd of March, 322 people exceeded 300 people for the first time, setting a new record high.



The number of people surpassing 200, which was not before the 5th wave, continues every day.


(* The number was 216 on May 18, 2021, but on this day, the number of people who had not been reported after Hyogo Prefecture died from March to May 2021 is reported together. The



number of dead people announced after January 2022 is 4402 by February 24th.



The number of people who died during the Delta strain period was 3483 in the four months from July to October 2021, which is already higher in the sixth wave of Omicron strain-based infections.



The Omicron strain is said to be less likely to become severe, and the case fatality rate is about 0.14%, which is lower than that of the previous virus, but the scale of infection is so large that the number of severe cases and deaths is high.



Most of the people who have died are elderly people, and it is said that infection often exacerbates the underlying disease.



According to the Ministry of Health, Labor and Welfare, of the 817 people who died in about one month from January 5 to February 8, 34.4% were in their 90s or older, 36.6% were in their 80s, 19.6% were in their 70s, and 60s. Is 4.0%, and 94.6% are in their 60s or older.

In Japan, the fifth wave of the summer of 2021 when the Delta strain spread was the timing of advanced vaccination, so it is said that the vaccine was able to prevent the death of many elderly people.



Although the effect of two vaccinations is effective in preventing the aggravation to a certain extent, the infection of the Omicron strain spreads to the elderly and some people become more severe when the effect has decreased after a long time from the vaccination. It is believed to be increasing.



In the spread of infection so far, the number of severely ill people peaked about two weeks after the peak number of infected people, and then the number of deaths has peaked, and there is a possibility that it will continue to increase in the future.



Professor Hiroshi Nishiura of Kyoto University said at an expert meeting of the Ministry of Health, Labor and Welfare on February 24, a total of 5517 people who are estimated to die from the new coronavirus from December 2021 to April 23, 2022. I showed the estimation result that there is a possibility of climbing to a person.



It is said that this estimate does not include the effects of the third vaccination, but if 60% of the elderly complete the third vaccination during February, the elderly will die 295. We can expect to reduce the number of people.

In some countries, the number of deaths has decreased, and in some countries, the number of deaths has risen again.

Overseas, while the number of deaths has finally started to decline in some countries, it has increased in others.



In the United States, according to CDC data, the number of deaths reported per day on average has exceeded 2000 for about a month since mid-January.



It peaked in early February and gradually decreased, falling below 2000 in mid-February, and as of February 23, it has reached more than 1600.

In the United Kingdom, the average number of deaths reported per day per week returned to 123 at the end of 2021, before the number of deaths began to increase, to 123 in the week leading up to February 16. ..



On the other hand, according to "Our World In Data", a website operated by researchers at Oxford University in the United Kingdom, the number of deaths per day is one week until February 23. In France, the number of people continues to be high at 233, exceeding the peak of about 110 people in late August 2021 during the Delta stock period.



In Germany, the number of deaths decreased in late January 2022, averaging about 140 per week, but the infection has spread rapidly again, and now it has increased again to 204.

What kind of person is getting sick?

It is said that many people with severe illness are elderly or have underlying illness.



At the expert meeting of the Ministry of Health, Labor and Welfare on February 24, the results of analyzing cases of severe illness from December 17, 2021 to February 17, 2022 were reported in Osaka Prefecture.



According to this,


the rate of severe illness in people with underlying illness was 2.33%,


which was significantly higher than 0.05% in those without underlying illness.



Here, as patients with underlying diseases at high risk of aggravation, patients with respiratory diseases such as diabetes and heart disease, COPD = chronic obstructive pulmonary disease, patients undergoing artificial dialysis, immunosuppressive agents and anti-viruses are listed. It lists patients who are using drugs.



By age group, even with underlying illness,


less than 1% of people in their teens to 40s became more severe, while


1.25% in their


50s, 2.14% in their 60s, and


▽ 70s. It was

3.71%,


▽ 80s 3.38%,


▽ 90s 1.63%,


▽ 100s 4.00%, etc.



The rate of death


was 0.04% in the absence of


underlying illness and 2.82% in the presence of underlying illness.



The expert meeting also reported data on the proportion of people who became severely ill or died in Hiroshima Prefecture.



According to it, the percentage of people who were mild when the infection was found became severe or died was 0.4% in the 6th wave, which was lower than 0.8% in the 5th wave.



The percentage of people who were initially mild but became severe or died


▽ Age over 80 years old 4.4%,


▽ Diabetes 2.1%,


▽ Heart and blood vessel diseases 2.7%,


▽ COPD 5.5%,


▽ Cancer 2.3%,


▽ Dementia 3.7 %

It was%.

"BA.2" 0.6% by January, but ...

A mutant virus called "BA.2", which is one of the Omicron strains, is being watched because it may affect the infection status.



Infections in the city have been reported in Japan as well.

Omicron strain "BA.1", which is spreading all over the world, has a part missing in the protrusion "spike protein" on the surface of the virus, but "BA.2" lacks this part. I know there are no parts.



Omicron strains may not be detected by some of the overseas inspection methods, and they are sometimes called "stealth omicrons", but in Japan they can be detected by another method, so this name is used. It is said that it will not hit.



However, it is necessary to analyze the genetic information to distinguish between "BA.1" and "BA.2".



According to the survey results released on February 16 by the National Institute of Infectious Diseases, 94 cases of "BA.2" were reported nationwide from the end of 2021 to January 30 in Japan, and Omicron. It is said that it accounts for about 0.6% of the total strain, but it may take time to analyze the gene, so it is a tentative result.



Professor Hiroshi Nishiura of Kyoto University, who specializes in theoretical epidemiology, commented on the analysis of BA.2 after the expert meeting of the Ministry of Health, Labor and Welfare held on February 24. We have not been able to grasp the actual situation of the spread in real time. A partial sample survey is sufficient, so a nationwide survey is necessary. "

What is the infectivity of "BA.2"?

How serious is it?

"BA.2" is considered to be even more infectious.



According to a research institute under the Danish health authorities, "BA.2" was about 20% of the new coronavirus detected in Denmark in the last week of 2021 in 2022 1. It is said that it was about 66% in the week from the middle of the month to the end of the month.



In addition, according to the health authorities in the United Kingdom, the number of mutant viruses that are considered to be "BA.2" in the United Kingdom increased from 5.1% on January 24, 2022 to 18.7% on February 6. ..



The average "onset interval" between the onset of one infected person and the next onset of the infected person was 4.09 days for the Delta strain, but 3.72 days for the Omicron strain "BA.1". , "BA.2" has an average of 3.27 days, which is about half a day shorter than "BA.1", and it is possible that it is related to the rapid spread of infection.



On the other hand, a group of Tokyo Medical and Dental University announced that as a result of analyzing 40 people infected with Omicron strain in Japan, more than 70% were "BA.1.1", a "BA.1" strain virus. ..



In countries where "BA.1" is the mainstream, such as Denmark, the replacement with "BA.2" has progressed quickly, while in countries where "BA.1.1" is the mainstream, the replacement may be slow, and we will continue to analyze it. It is said that it is necessary.



An expert meeting of the Ministry of Health, Labor and Welfare said on February 24, "There are no signs so far, but it is necessary to be careful that the infection may start to increase again if it is replaced in the future."



There are also reports from overseas that there is no difference in the risk of hospitalization for "BA.2".



According to a report from a Danish research institute, there is no difference in the risk of hospitalization, and 47 cases of re-infection with "BA.2" after being infected with "BA.1" have been reported, but most of them are vaccinated. He said that he was a younger generation who had not been struck, had mild symptoms, and no one was hospitalized.



Health officials in the United Kingdom have reported no cases of re-infection with "BA.2" after being infected with "BA.1", although data are still limited.



In addition, WHO states that there is no evidence that the risk of aggravation due to "BA.2" is higher than that of "BA.1".



Regarding the effect of the vaccine, the health authorities in the United Kingdom said that the effect of the vaccine to prevent the onset was


▽ more than 25 weeks after the second vaccination, and after about half a year or more, it was 9% in "BA.1". 13%


for ".2" and 70% for "BA.2" compared to 63% for "BA.1" two weeks after the third booster inoculation, indicating that there was no difference in the vaccine effect. is.

Inflammation of the upper respiratory tract is easy, and symptoms of cough, throat, and nose are also present.

Regarding the Omicron strain, the WHO = World Health Organization says that although it is prone to inflammation of the upper respiratory tract such as the nose and throat, for many people, the risk of reaching the lungs and becoming severe is lower than other mutant viruses.



As of January 24, the National Institute of Infectious Diseases has released data on more than 3,600 people registered in the system "HER-SYS" that aggregates information on people infected with the new coronavirus.



At the time of notification, the symptoms seen with Omicron strains were


▽ fever 66.6%,


▽ cough 41.6%,


▽ general malaise 22.5%,


▽ headache 21.1%,


▽ non-cough respiratory symptoms 12.9%,


▽ Nausea and vomiting are 2.7%, and


diarrhea is 2.3%.



So far, 0.8% of people have complained of the olfaction and taste disorders that are characteristic of the new coronavirus.



Other domestic and overseas surveys have also shown symptoms of cough and sore throat, runny nose and stuffy nose, and the Japanese Society of Otolaryngology Head and Neck Surgery is suffering from hay fever every year as it is confusing with the symptoms of hay fever. People who have hay fever are encouraged to see a medical institution as soon as possible before symptoms appear.

Verification of sequelae of Omicron strain is yet to come

There is growing interest in each country about the extent of sequelae after infection with the Omicron strain, but it is not yet clear.



Regarding the sequelae of the new coronavirus called "Long COVID," WHO states that "a symptom that begins 3 months after the onset and lasts for at least 2 months."



With the conventional new coronavirus, about 10% to 20% of people who experience infection have sequelae such as malaise, shortness of breath, and cognitive dysfunction, which are said to "generally affect daily life."



"There seems to be no connection between the severity of the initial infection and the subsequent sequelae," he said.



It's been more than three months since the Omicron strain was first reported in South Africa, and it is expected that the sequelae will be examined in the future.

Discussion of "after Omicron stock"

On January 26, a group of experts providing scientific advice on infectious disease control to the British government issued a statement summarizing the medium- to long-term outlook for the future.



Although it is difficult to predict new mutant viruses, it is almost certain that a wave of epidemics will come again in the future, and the pathogenicity will not necessarily be alleviated.



He said that it could be years before the epidemic could be predicted, and that it is necessary to maintain a monitoring and surveillance system to grasp and report the infection status.

Comparison with previous mutant viruses

Based on information from WHO, the National Institute of Infectious Diseases, and public institutions in each country, what is known now, such as infectivity and pathogenicity, is compared with other "variant of concern = VOC". I summarized it.

▽ Infectivity According to


the WHO weekly report, the Omicron strain is more likely to spread than the conventional mutant virus.



▽ Pathogenic


Omicron strains are said to have a lower risk of hospitalization and aggravation than Delta strains.



However, the scale of the spread of infection is large, and the number of hospitalized people and the number of people who are becoming more serious are increasing, and the burden on medical institutions is increasing.



▽ Risk of re-infection


WHO states that there are mutations in the Omicron strain that make it easier for people with immunity to re-infect due to vaccines and past infections.



Imperial College London in the United Kingdom reports that the risk of reinfection with Omicron strains is 5.41 times higher than with Delta strains.

▽ Effect of vaccine (Pfizer Moderna's mRNA vaccine)


The effect of the vaccine is reduced for the Omicron strain, but it is said that the effect will be increased again by the third booster vaccination of the vaccine.



According to data from the UK health authorities, Pfizer and Moderna mRNA vaccines for Omicron strains dropped to about 10% after 20 weeks from two doses, but Pfizer or Moderna boosters were given. Then, after 2 to 4 weeks, the effect of preventing the onset increased to 65% to 75%.



The effect of reducing the risk of hospitalization due to severe illness is higher than the effect of preventing the onset.

Analysis of people vaccinated with Pfizer, Moderna, and AstraZeneca shows that the effect of preventing hospitalization is 72% for 2 to 24 weeks after two vaccinations and 52% for more than 25 weeks, 3 After the second booster vaccination, it was 88% after 2 weeks.

アメリカのCDCのデータでは、ワクチンを打っていない人と比較して、ファイザーやモデルナの「mRNAワクチン」で入院を防ぐ効果は、デルタ株の時期には、3回目の追加接種のあとだと、2か月までだと96%、4か月以上たっても76%でした。

オミクロン株の時期には、2回目の接種から2か月までだと入院を防ぐ効果は71%、5か月以上たつと54%となっていましたが、3回目の接種を行うとオミクロン株に対しても入院を防ぐ効果は上がり、接種から2か月以内だと91%、4か月から5か月でも78%になっていました。

CDCは、3回目の接種が重要で、未接種者はできるだけ早くワクチンを接種する必要があるとしています。

治療薬の効果重症化を防ぐために感染した初期に投与される「抗体カクテル療法」は、効果が低下するとされ、厚生労働省はオミクロン株では投与を推奨しないとしています。

一方で、軽症患者用の飲み薬「ラゲブリオ(一般名モルヌピラビル)」や、新たに承認された「パキロビッドパック(一般名ニルマトレルビル/リトナビル)」、それに軽症から重症の患者まで投与される「レムデシビル」など、ウイルスの増殖を防ぐ仕組みの飲み薬には影響が出ないと考えられています。

また、WHOは、重症患者に使われる免疫の過剰反応を防ぐ薬やステロイド剤は、引き続き効果が期待されるとしています。

専門家は

今後の見通しについて厚生労働省の専門家会合の脇田隆字座長は、2月24日の会合のあと「新規感染者数の減少傾向を保つことが、医療の状況の改善につながるが、今は、ぎりぎり減少傾向になっている状態だ。今後、人々の接触機会が増えるなど、少しのきっかけで、再び増加傾向になって医療への負荷につながると考えられる。感染状況を改善させて、それを継続させることが非常に重要だ」と述べました。

In addition, Professor Atsuo Hamada of Tokyo Medical University, who is familiar with infectious diseases overseas, said about "BA.2", "At this point, it is considered that" BA.2 "is not widespread in Japan. There are no reports that "BA.2" has increased the number of severely ill people or the vaccine has become less effective than "BA.1", so it is considered that there is no change as a countermeasure. However, "BA.2" will spread. There are countries that do not, and there are countries that do not, and the detailed reason why they are different is not yet known, and it is undeniable that the epidemic will be prolonged if it spreads in Japan, so it is necessary to strengthen monitoring sufficiently in the future. There is. "

Measures do not change

Even with the Omicron strain, the infection route is the same as before, and the main infections are infection by flying, and very small flying flying in a closed room called "micro flying" or "aerosol".



There is also contact infection by touching the nose or mouth with a hand with the virus.



Omicron strains were also infected through eating and drinking, such as year-end parties with colleagues at work at restaurants and dinner with relatives at home, and cases of infection through work in a dense environment at work were also reported. I am.

Shigeru Omi, chairman of the government subcommittee, said that infections in situations where the mask was removed or inadequately worn, such as a "nose mask," were far more common than expected, and he called for a non-woven mask to cover the nose. I am.



In addition to vaccination, the Ministry of Health, Labor and Welfare's expert meeting has spread the infection due to events where many people gather, so one secret meeting will be held toward the end of the year when events such as graduation ceremonies and spring break will be held. However, we are calling for thorough infection control measures such as avoiding crowded places and high-risk situations when going out, properly wearing non-woven masks, disinfecting fingers, and ventilation.

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