It seems that the "eighth wave" of the new corona has finally passed its peak, but a new mutated virus that has been rapidly expanding in the United States since the end of last month has been detected in Japan.
It is said that the immunity made by vaccines and infections is the most difficult to work among the mutation viruses so far.
Will it lead to further spread of infection?
Should I get the vaccine?
I have summarized what I have learned.
“XBB.1.5” Rapid expansion in America
"XBB.1.5" is a mutant virus "XBB" that combines two types of "BA.2" that spread from around the spring of 2022 among the Omicron strains, and further mutations have been added.
In the United States, the rate of detection has expanded rapidly from around December 2022, mainly in the eastern part of the country such as New York, making it the most mutated virus.
According to the Centers for Disease Control and Prevention (CDC) in the United States, an estimated 49.1% of people newly infected with the new coronavirus in the week ending January 21 were detected with "XBB.1.5". .
According to the weekly report of WHO = World Health Organization on January 11, the detection of "XBB.1.5" has been reported from 38 countries so far.
Data on 'XBB.1.5' are still limited, and according to the January 19 weekly report, the entire 'XBB' lineage accounted for 8.36% of the novel coronaviruses reported worldwide in the last week of the year. It is
WHO “may lead to an increase in global cases”
On January 11, WHO released the risk assessment of "XBB.1.5".
According to this, the spread of infection is relatively easy to spread in the United States, but further analysis is required.
▽ Preliminary experimental data show that the ability to escape from immunity obtained from past infections and vaccinations is higher than that of the Omicron strain mutant virus so far.
▽ There is no clinical data yet regarding the severity of infection.
However, no mutations have been identified that could lead to changes in severity.
On top of that, although the data is currently limited, it 'may lead to a global increase in cases.'
Is it a mutation that easily sticks to human cells?
A researcher group "G2P-Japan" led by Professor Kei Sato of the Institute of Medical Science, the University of Tokyo, created an artificial virus by reproducing the characteristics of "XBB.1.5" as a paper before being peer-reviewed. We published the results of the experiment.
After vaccination, the research group used the blood of people infected with the Omicron strain `` BA.5 '', which was the mainstream in the 7th wave after the summer of 2022, to investigate the immune response to `` XBB.1.5 ''. I was.
As a result, the activity of the neutralizing antibody that suppresses the virus was only about 1/10th of that against BA.5, demonstrating its ability to escape immunity.
In addition, the results showed that the infectivity may be increasing.
When the new coronavirus infects humans, it attaches to a protein called ACE2 on the surface of cells.
Viruses are more infectious when they easily attach to human cells.
"XBB.1.5" has a new mutation "F486P".
According to Professor Sato, due to this mutation, "XBB.1.5" had a 4.3-fold increase in the ability to bind to proteins on the surface of cells compared to the non-mutated mutant virus.
In previous mutant viruses, it was difficult to achieve both ``escape from neutralizing antibodies'' and ``increase binding strength'', but ``XBB.1. doing.
“A big mutation that has never been seen before”
Professor Sato
: “The ability to evade immunity has increased, and it is thought that the addition of further mutations to “XBB”, which was, so to speak, the “completed form”, has increased the ability to infect cells, making it easier to spread. Such a large mutation Until now, there have been very few cases.”
On the other hand, the severity and virulence of infection are still poorly understood.
Infecting hamsters with 'XBB' virus from an infected person caused lung inflammation and damage to the same extent as previous Omicron strains, they reported.
Professor Sato said that "XBB" does not seem to have increased ability to cause symptoms.
in various viral coexistence situations
"XBB.1.5" is considered to be easy to escape immunity and highly infectious, but so far it has not spread widely outside the United States, and even in the United States, it has not caused an explosive nationwide infection.
Also, in the world, and in Japan as well, a specific mutated virus does not account for almost everything, as it has been until now, and various viruses coexist.
In Japan, according to the materials presented by the Tokyo Metropolitan Government at the monitoring meeting on January 19, 22 cases of "XBB.1.5" have been detected in Tokyo so far.
In the week leading up to January 2nd, the rate of detection was 0.3%, which is not a large increase.
According to the data released at the monitoring meeting in Tokyo, all of the mutant viruses detected in the week leading up to the beginning of January are one of the Omicron strains
. Mainstream from summer)
▽ ``BQ.1.1'' 16.2% (Mutation added to ``BQ.1'')
▽ ``BF.7'' 14.2% (Mutation added to ``BA.5'', likely to spread in China)
▽ ``BN. 1” 10.4% (mutated to “BA.2.75”)
▽ “BQ.1” 3.6% (mutated to “BA.5”)
▽ “BA.2.75” 3.2% (mutated to “BA.2”)
▽“BA.2” 1.3% (mainstream from spring to summer 2022)
▼[“XBB.1.5” 0.3%]
▽“XBB” 0.2%.
According to a group such as Associate Professor Hiroaki Takeuchi of Tokyo Medical and Dental University, who is investigating the genes of the new coronavirus's mutated virus, "XBB.1.5" has not been detected from inpatients at Tokyo Medical and Dental University Hospital. .
When we analyzed the genes of the new coronavirus in 13 hospitalized patients during the two weeks until January 9,
▽ "BQ1.1" from 3 people and
▽ "BF.7" from the Omicron strain were found .
▽"BN.1" was detected from 5 people, but
▼
【"XBB.1.5"】 was not detected.
Most of the 13 patients were over the age of 60 and had pre-existing medical conditions, but none of them became severe.
Associate Professor Takeuchi
: “At the moment, 'XBB.1.5' is not in a situation where it will spread immediately, and it is not known if it will become the mainstream of the next resurgence of infection in Japan. Isn't it
Will it lead to a resurgence of infection?
What will happen if "XBB.1.5" flows further in the future?
Professor Nishiura of Kyoto University is wary.
Professor Nishiura
: "'XBB.1.5' tends to widely avoid the power of immunity due to neutralizing antibodies acquired through previous vaccinations and infections. Currently, domestic infections are on a downward trend. However, 'XBB.1.5' is considered to have the risk of causing a new epidemic again."
Atsuro Hamada, a specially appointed professor at Tokyo Medical University who is familiar with the situation of overseas infections, believes that there is a good chance that Japan will gradually replace it with "XBB.1.5" in the future.
Project Professor Hamada
: "It's not that the number of infected people is increasing in the United States, but that the rate of detection of ``XBB.1.5'' is increasing.At first, there were many in the eastern part of New York State, but the western part It seems that the speed of expansion is not so fast.It is certain that it is spreading, so it may take some time, but it is enough that it will be replaced by "XBB.1.5" in Europe and Japan. We must continue to monitor the situation, including the situation in the United States, to see if the number of infected people will increase rapidly as the replacement progresses."
“Inoculate against the Omicron strain”
In addition, regarding the impact on the future infection situation, it should be assumed that the number of infected people will increase again.
Specially Appointed Professor Hamada
"In Japan, there is a growing view that the 8th wave has peaked out, but the situation where tens of thousands of people are infected every day will continue. 'XBB.1.5' is in full swing. It is possible that the "8th wave" will be prolonged if it hits the target, or that the "9th wave" will occur after the number of infected people has decreased. I don't think it will happen, but I think it's better to expect to some extent that the number of infected people, who had been on a downward trend, will increase again. No. It is important to get the vaccine against the Omicron strain to boost your immunity.In order to prevent the severity of the disease, I would like people who have not yet received the booster vaccination to get it as soon as possible.”