Omicron strain, which has been considered to be less likely to become severe.
However, while the number of infected people continues to be at a record high, the number of severely ill patients continues to increase.
The number of deaths reported per day exceeds 100, higher than the peak during the fifth wave of the spread of the Delta strain.
What kind of person is getting sick?
Is the effect of priority measures such as spread prevention taken for the purpose of controlling infection also appearing in Omicron strains?
What is the impact on the infection status of the different strains of Omicron strain "BA.2" that have begun to be reported in Japan?
I have summarized what I have learned.
(As of February 9, 2022)
Number of deaths per day beyond the time of Delta stock
The spread of this new coronavirus caused by the Omicron strain.
Although the pace of expansion has slowed slightly, it remains at a record high.
The number of deaths reported per day was 34 on January 26, 2022, two weeks ago, but on February 4, 103 and over 100, and on February 9. Renewed a record high of 162 people.
It is more than 89 people on September 8, 2021, which was the highest number in last summer when Delta stocks spread.
In the United States, the CDC = Centers for Disease Control and Prevention summarizes that the number of deaths reported per day continues to exceed 2000, except on weekends when reports are low.
According to the CDC, although the severity of the Omicron strain is low, the number of inpatients is increasing, which puts a burden on the medical system and the number of deaths is considerable.
According to "Our World In Data", a website run by researchers at Oxford University in the United Kingdom, the number of deaths per day will be in the week until February 8th.
▽ About 2500 people in the United States
▽ About 330 people in France ▽ About
100 people in Japan
.
At the time of Delta stocks,
▽ in the United States, about 2000 people in late September 2021
▽ in France, about 110 people in late August
peaked, and now it is above the level at that time.
Even if it is hard to get serious, the scale of infection is too "large"
The number of critically ill patients continues to grow.
The number of critically ill patients in Japan was 1141 as of February 8, 2022.
This is the same level as the 1138 people on August 8, 2021, when the closing ceremony of the Tokyo Olympics was held.
At this time, a state of emergency was issued to six prefectures.
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.
According to a report issued at an expert meeting of the Ministry of Health, Labor and Welfare on February 9, 2022, an analysis of nearly 200,000 infected persons reported by February 5 during the 6th wave in Osaka Prefecture shows. The severity rate is 0 points 08%.
Similarly, at the expert meeting, the results of analyzing the symptoms of 2214 people infected by January 31 in the "Miyako / Yaeyama Medical Area" in Okinawa were also reported. 1.9%, moderate 1 with shortness of breath and pneumonia was 3.6%, and mild or asymptomatic was 94.5%.
Although the rate of serious illness is low, the scale of infection is so large that the number of severely ill people is increasing, putting pressure on the medical system.
The fifth wave of infection last summer when the Delta strain spread was the timing of advanced vaccination, and it is said that the vaccine was able to prevent the deaths of many elderly people.
Although the effect of two vaccinations is effective in preventing the aggravation to a certain extent, it is thought that the Omicron strain spreads and the number of people who become aggravated is increasing when the effect has decreased after a long time from the vaccination. I am.
The bed usage rate is increasing day by day, and as of February 8, it is 81.4% in Osaka prefecture, 57.8% in Okinawa prefecture, 55.8% in Tokyo, and so on.
In addition, there are cases where it is difficult to transport general emergency patients other than the new coronavirus, and some university hospitals that examine the most severe emergency patients in Tokyo can accept only about 60% of the usual patients. It's coming.
What kind of person is getting sick?
It is said that many people with severe illness are elderly or have underlying illness.
According to the materials submitted to the expert meeting of the Ministry of Health, Labor and Welfare, the rate of worsening pneumonia and becoming "moderate 2" or higher requiring oxygen administration from January 1st to 20th, 2022 became severe. It was 0.09% for those without the risk factor, but 1.22% for those with the risk factor, which is more than 13 times higher.
Risk factors include
"chronic obstructive pulmonary disease," "diabetes," "dyslipidemia," "hypertension," "chronic kidney disease," "cancer," "obesity," and "smoking." The percentage of people with moderate disease 2 or higher was as high
as 0.81% for one risk factor
, 2.13% for
two, 3.63% for
three, and 4.70%
for four or more. ..
By age,
▽ people with at least one risk factor are 0.155% under 40 years old ▽
0.37% for people in their 40s ▽
0.61% for people aged 50 to 64 years old ▽ 4.43%
for people aged
65 and over
It was so high.
Significant hospitalization risk due to additional vaccination ↓
Even Omicron strains are thought to be effective with booster vaccination.
On January 21, the CDC = Centers for Disease Control and Prevention in the United States released an analysis result that the effect of preventing hospitalization increases to 90% even for Omicron strains.
More than 6 months after the second dose of Pfizer or Moderna's "mRNA vaccine", the effect of preventing hospitalization was 81% when the Delta strain was dominant, while it was when the Omicron strain was dominant. Was 57%.
However, after the third inoculation, the delta strain time increased to 94% and the omicron strain time increased to 90%.
In addition, the rate of hospitalization for those who have not received the booster vaccine is significantly higher than that for those who have received the booster vaccine, and it is analyzed that it is 44 times higher for those aged 50 to 64 and 49 times higher for those aged 65 and over. It is also announced.
The CDC states that a third dose is important to prevent worsening of symptoms, and unvaccinated individuals should be vaccinated as soon as possible.
Inflammation of the upper respiratory tract and symptoms of cough and throat and nose
Omicron strains have different symptomatic tendencies than previous Delta strains.
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.
Symptoms seen with Omicron strains at the time of notification are
▽ fever 66.6%
▽ cough 41.6%
▽ general malaise 22.5%
▽ headache 21.1%
▽ non-cough respiratory symptoms 12.9%
▽ nausea and vomiting 2.7 %
▽ 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.
In addition, the National Institute of
Infectious
Diseases
investigated 122 people in detail in an epidemiological
survey
. And dysgeusia were around 1% each.
It is said that more people complain of sore throat and fewer people complain of no smell or taste.
In addition, because of the symptoms of runny nose and stuffy nose, the Japanese Society of Otolaryngology Head and Neck Surgery calls for people suffering from hay fever to see a medical institution as soon as possible before the symptoms appear. increase.
After the priority measures, the speed of infection spread will slow down ...
It has already been one month since the priority measures such as prevention of spread were applied to the three prefectures of Okinawa, Hiroshima, and Yamaguchi as measures against the spread of infection by Omicron strains, and it has been nearly three weeks since it was spread to the metropolitan area.
According to the data given at the expert meeting of the Ministry of Health, Labor and Welfare, the number of people in the downtown area at night was
halved in Okinawa prefecture compared to December 2021 as of late January
▽ halved in Hiroshima prefecture
▽ 30 in Yamaguchi prefecture. %
Decreased.
In addition,
▽ decreased by more than 30% in Tokyo ▽ decreased by
about 30% in Aichi prefecture
.
In the three prefectures where the first priority measures were issued, the number of infections has been decreasing.
However, in many areas, the rate of spread of infection has only slowed.
In Okinawa, the highest number of infected people per day was 1829 on January 15, when the population was close to 700 per 100,000.
Since then, it has been declining, but as of February 8th, which is more than three weeks old, there are more than 290 people per 100,000 population.
It is finally below the peak of 320 people in the summer of 2021 when Delta stocks spread.
The speed at which the infection subsides is gradual, but data presented by Professor Hiroshi Nishiura of Kyoto University at an expert meeting on February 2 suggest that it has passed its peak in Okinawa Prefecture.
In addition, according to the data released on February 9, the effective reproduction number, which indicates how many people one person spreads to, dropped to around "1" in the metropolitan area and Osaka, and sometimes exceeded "2". It has been on a downward trend since early January 2022.
On February 2, the expert meeting stated that the infection situation nationwide "is expected to continue to spread while the rate of increase is slowing down."
Overseas, in the United Kingdom, the number of newly infected people in a week exceeded 1 million around January 10, and then in the week until January 18, it was about 674,000, compared to the previous week. It decreased by about 40%.
After that, it has been flat for a while, and then it has decreased again to more than 509,000 in the week until February 8.
Is it highly infectious?
What I learned from "BA.2"
On the other hand, a mutant virus called "BA.2", which is one of the Omicron strains, is being watched as it may affect the infection status.
It has begun to be reported not only in Japan but also in Kobe City and Tokyo.
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 inspection methods performed overseas, and it is sometimes called "stealth omicron", but in Japan, it can be detected by another method, so this name is used. It is said that it will not hit.
"BA.2" is considered to be highly infectious.
According to a laboratory under the Danish health authorities, "BA.2" was about 20% of the new coronavirus detected in Denmark in the last week of 2021 in January 2022. It is said that it was about 66% in the week from the middle to the end of the month.
In addition, as a result of analyzing the infection at home for about one month until mid-January 2021, the rate of secondary infection at home was 29% for "BA.1" and 39% for "BA.2". If so, it may be easier to spread.
On the other hand, although the proportion of "BA.2" is increasing in Sweden, Norway, and the United Kingdom, which are neighboring to Denmark, it is only about 10% to 20% of all Omicron strains.
Professor Hiroshi Nishiura of Kyoto University said, "Due to the epidemic of'BA.2', the epidemic curve has become two-tiered in Denmark, and the rise has started again after the number of infected people has decreased in South Africa. Even if the number of infected people begins to decline, there is a risk of future increases and spreads. It is more important to understand the mechanism in order to see the tightness of the medical system. "
On the other hand, even with "BA.2", the risk of aggravation is considered to be the same as with "BA.1".
On February 7, a group at the International University of Health and Welfare, which treated 22 patients infected with "BA.2," announced that they were all mild or asymptomatic.
Although most of them were vaccinated and no one was at risk of becoming severe, the treatment policy itself seems to be the same as "BA.1".
British health officials say that vaccines are effective in preventing the onset.
More than 25 weeks after the second inoculation, 9% in "BA.1" after about half a year, 13% in "BA.2",
and "BA. 2 weeks after the third booster inoculation". In "BA.2", it was 70%, compared to 63% in "1", and there was no difference in the effect of the vaccine.
Concerns in countries where childhood infections are widespread
With the Omicron strain, the spread of infection in children, which was previously low, continues.
According to the website of the Ministry of Health, Labor and Welfare, the number of newly infected people under the age of 10 was 149 in the week until December 28, 2021, but by January 4, 2022, it was 353, January 11. The number has continued to increase to 2,238 by January 18, 12,947 by January 18, 41,863 by January 25, and 67,564 by February 1.
In the United States, approximately 4.2 million children have been confirmed to be infected in 2022.
By February 3, the number of newly infected children in the week was more than 630,000, which is declining but more than double the peak of the Delta strain period.
The American Academy of Pediatrics reports that children with severe symptoms have a rate of 0.1 to 1.5% hospitalization and a mortality rate of 0 to 0.01%.
Even in Japan, the age of vaccination has been reduced to 5 years old.
In Pfizer's clinical trials, 90.7% was effective in preventing the onset between the ages of 5 and 11, and the symptoms after vaccination were generally mild to moderate.
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 susceptible to spread than previous mutant viruses.
▼ Pathogenicity
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 reinfection
WHO states that the Omicron strain has mutations 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.
▼ Vaccine effect (Pfizer Moderna's mRNA 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.
▼ Effect of therapeutic drug
"Antibody cocktail therapy," which is given in the early stages of infection to prevent aggravation, is said to be less effective, and the Ministry of Health, Labor and Welfare does not recommend administration for Omicron strains.
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）」や中等症以上の患者用の「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
厚生労働省の専門家会合のメンバーで国際医療福祉大学の和田耕治教授は「オミクロン株では多くの人にとって重症化や死亡のリスクは下がっているが、特に75歳以上ではどうしてもリスクがあり、高齢者に感染が広がれば去年夏の第5波よりも亡くなる人が多くなるかもしれない。今後、3月の年度末、4月の新年度と、再び人との接触機会が大きく増加するタイミングが近づいている。それまでに、少なくとも65歳以上の高齢者に、なるべく早く3回目のワクチン接種を行うことが必要だ」と話しています。
対策は変わらない
今の感染拡大の状況の中で、専門家は対策をより徹底するよう呼びかけています。
オミクロン株の感染経路もこれまでと変わらず、飛まつによる感染、「マイクロ飛まつ」や「エアロゾル」と呼ばれる密閉された室内を漂う、ごく小さな飛まつが主となっています。
ウイルスがついた手で鼻や口などを触ることによる接触感染もあります。
オミクロン株でも、飲食店での職場同僚との忘年会や、自宅での親族との会食など、飲食を通じた感染が見られたほか、職場での密な環境での作業を通じて感染するケースも報告されています。
The chairman of the government subcommittee, Mr. Omi, said that the number of infections was much higher than expected in situations where the mask was removed or inadequately worn, such as a "nose mask," and he called for a non-woven mask to cover the nose. increase.
In addition to vaccination, the Ministry of Health, Labor and Welfare's expert meeting also calls for continued basic measures such as wearing masks, especially during conversations, disinfection and hand washing, and avoiding ventilation and tightness.