A new mutant virus "Omicron strain" of the new coronavirus.

Community-acquired infections have been confirmed in various places, and infections are spreading at an unprecedented pace in Okinawa.

In Western countries, the number of infected people has reached a record high, and the strength of infectivity has become clear.

Although it has been reported that the risk of aggravation is low, a rapid spread of infection may place a heavy burden on medical institutions.

Now that the spread of infection is imminent in Japan, I have summarized what I have learned.


(As of January 5, 2022)

Omicron strain, community-acquired infection one after another

The first case of what appears to be a community-acquired Omicron strain was found on December 22, 2021.

It was in Osaka prefecture.



Since then, it has been confirmed in Tokyo, Aichi, Okinawa, etc., and as of January 4, there are 18 prefectures where there is a possibility of community-acquired infection.

Community-acquired infections mean that "infections that do not follow the route" are occurring in the city, and there is a risk that the infection will spread to the region in the future.



In Okinawa Prefecture, the number of infected people is doubling every day, and it has been pointed out that the Omicron strain may have an effect.



As the number of people increases during the year-end and New Year holidays and the number of people moving home is increasing, the infection itself is on the rise, but the influence of the Omicron strain may lead to the sixth wave of infection spread. I'm worried about it.

Omicron strain "strongly infectious"

The Omicron strain has been evaluated to be more infectious than the mutant viruses such as the Delta strain that have been reported so far.



Even in Western countries, where Delta strains occupied almost all of them, they were rapidly replaced in about a month, and Omicron strains are becoming the majority.

In the United Kingdom, a cumulative total of approximately 247,000 people have been confirmed infected with the Omicron strain by December 30, and about 95% of the new coronavirus detected in most parts of England is Omicron. It is believed to be a stock.



And on January 4, the number of infected people per day exceeded 200,000, setting a new record high.



In France as well, the number of infected people per day exceeds 270,000, which is a record high.

In the United States, the number of people infected with the new coronavirus reported on January 3rd and 1st was about 1.08 million, exceeding 1 million, the highest ever.



There seems to be an expansion of Omicron strains in the background, and President Biden said, "Omicron strains are extremely infectious and the number of infected people is expected to continue to increase in the coming weeks. It's going to be tough. "

According to the CDC = Centers for Disease Control and Prevention, the proportion of Omicron strains in the United States was estimated to be about 0.6% in the week up to the 4th of last month, 77.0% in the week up to the 25th, and in the week up to the 1st of this month. It is said that it has almost replaced with 95.4%.



On the other hand, the incubation period from infection to onset is around 3 days according to the provisional data of the active epidemiological survey in Japan, and 3.6 days according to the analysis of infected cases at Korean health facilities. It is said to have a shorter incubation period than the Delta strain.

Is it "mild even if infected"?

There have been a series of reports that the Omicron strain has a low rate of becoming severe even if infected.



On January 4, the head of the WHO = World Health Organization said that although the symptoms of the Omicron strain are more likely to cause inflammation of the upper respiratory tract such as the nose and throat, there is a risk that it will reach the lungs and become more severe than other mutant viruses. He expressed the view that it was low.



On the other hand, he is cautious, saying, "Further research is needed to prove it."

In the United Kingdom, by December 30, more than 212,000 people had been confirmed infected with the Omicron strain in England, 981 were hospitalized, and 75 died.



According to UK health officials, the risk of being hospitalized with Omicron strains is one-third that of Delta strains.



People who have been vaccinated for 14 days or more after the second vaccination are 65% less likely to be hospitalized than those who have not been vaccinated, and those who have been vaccinated for the third booster for 14 days or more. It was 81% lower.

On the other hand, health officials in the United Kingdom say that the low risk of aggravation does not necessarily mean that the burden on medical institutions will be reduced because the Omicron strain has the property of escaping the speed of spread and immunity. Is emphasized.



In addition, it takes a certain amount of time from the increase in the number of infected people to the increase in the number of people who become severely ill or die.



In a weekly report released on December 28, WHO said, "Early data from the United Kingdom, South Africa and Denmark suggest that Omicron strains have a lower risk of hospitalization than Delta strains, but oxygen inhalation and artificial respiration. We need more data to see the severity of respiratory use and death. "

Vaccine effect

It has been reported that the Omicron strain can be transmitted even to those who have been vaccinated.

Data from UK health authorities showed that Pfizer and Moderna mRNA vaccines were 65-70% more effective against the onset after 2-4 weeks of two doses, compared to 20%. After a week, it dropped to about 10%.

On the other hand, when a person who received two doses of Pfizer vaccine received a third booster dose of Pfizer or Moderna, the effect of preventing the onset increased to 65% to 75% after 2 to 4 weeks.



However, it dropped to 55-70% after 5 to 9 weeks and to 40-50% after 10 weeks.

On the other hand, it is highly effective in reducing the risk of hospitalization due to severe illness.



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.

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.

Infectious

It has been pointed out that the Omicron strain may be more infectious in terms of the number of mutations in the spike protein, but it is actually expanding at an unprecedented pace in each country.

Pathogenicity

▽ "Alpha strain"


→ High risk of hospitalization / severe / death



▽ "Beta strain"


→ High risk of hospitalization / high mortality rate at admission



▽ "Gamma strain"


→ High risk of hospitalization / severe



▽ "Delta strain"


→ Possibility of high risk of hospitalization



▽ "Omicron strain"


→ Is the risk of hospitalization low?

There have been a series of reports from various countries that Omicron strains have a lower risk of becoming more severe than Delta strains.



However, WHO has a certain period of time after infection until it becomes severe, and it becomes mild due to infection of the Omicron strain in people who have been vaccinated or who have been infected so far. It indicates the idea that you need to look carefully, as it may be.

Risk of reinfection

▽ "Alpha strain"


→ Maintains the function of the antibody that suppresses the virus, is the risk of reinfection the same as the conventional strain?



▽ "Beta strain"


→ The function of the antibody that suppresses the virus decreases, the function of the cells that attack the virus is maintained



▽ "Gamma strain"


→ The function of the antibody that suppresses the virus is slightly reduced



▽ "Delta strain"


→ The function of the antibody that suppresses the virus is reduced



▽ "Omicron strain"


→ The risk



of reinfection increases

It is said that there is a mutation that makes it easier for people who have it to re-infect.



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 mRNA vaccine)

▽ "Alpha strain"


→ No change in infection prevention / onset prevention / aggravation prevention



▽ "Beta strain"


→ No change in onset prevention / aggravation prevention



▽ "Gamma strain"


→ No change in infection prevention / onset prevention / aggravation prevention



▽ "Delta strain"


→ Infection prevention, onset prevention, and aggravation prevention are the same

(


reports that infection prevention and onset prevention are reduced)



▽ "Omicron strain"


→ Report that there is a decrease in onset prevention effect and aggravation prevention effect There is also a report that the onset prevention effect and the aggravation prevention effect are improved by the third inoculation.

It has been reported that the Omicron strain is infected even in people who have completed vaccination.



Although the onset prevention effect decreases with time after inoculation, there are data that the effect of preventing aggravation is maintained to some extent.



In addition, there are reports that the effect of preventing the onset and the effect of aggravation are improved by the third booster vaccination.

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.



The American pharmaceutical company "Regeneron" that developed it issued a statement on December 16 that "it will be less effective against Omicron strains".



On the other hand, it is thought that there is no effect on the medicines that are taken to prevent the growth of the virus.



In addition, WHO says that drugs and steroids used in critically ill patients to prevent immune overreaction will continue to be effective.

Transmission route

The main route of infection with the new coronavirus is a small flying eyelet or a small flying eyelet that floats in a closed room called "micro-flying eyeball", and contact infection by touching the nose or mouth with a hand with the virus has also been reported. ..



The Omicron strain may be more infectious, but it is believed to be a similar route of transmission.

Professor Kazuhiro Tateda "Possible replacement in Japan next month"

Professor Kazuhiro Tateda of Toho University, a member of the government's subcommittee on measures against the new coronavirus, said, "There are community-acquired infections of Omicron strains in various places, and there is a possibility that all domestic viruses will be replaced by Omicron strains in February. It has been pointed out that Omicron strains are less severe than Delta strains, but it is reported that their infectivity is 3 to 4 times higher. When the number of infected people increases explosively, they are hospitalized at a certain rate. It should be noted that some people will get sick and some will become seriously ill, which will lead to tight medical care. Even for Omicron strains, we will continue to thoroughly implement basic infection control measures. At the same time, it is important to use the mask properly and to keep ventilation even in winter. You should be careful about the spread of the infection in the eating and drinking place, and you should avoid a large number of people and long meals. " I'm talking.

Measures do not change

The Omicron strain is currently being researched around the world on its infectivity and pathogenicity, and WHO and the National Institute of Infectious Diseases will update the information.



The measures we can take are the same as before.



In addition to promoting vaccination, the Ministry of Health, Labor and Welfare's expert meeting is also calling for continued basic measures such as wearing masks, disinfecting and washing hands, and avoiding ventilation and tightness, especially during conversations.

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