Infection with the new coronavirus is gradually increasing again.

"BA.2", which is one of the Omicron strains and is said to be more infectious, is expected to become the mainstream in the next "7th wave".

Furthermore, another mutant virus "XE" gradually spread in the United Kingdom and other countries, and was confirmed by quarantine for the first time in Japan.

What is the current status of new mutant viruses and what are the necessary countermeasures?

■ "BA.2" Spreads around the world

The new coronavirus is constantly changing as it spreads around the world.

Among them, the virus called "BA.2", one of the Omicron strains, is the most widespread in the world.

From "BA.1", genes such as "spiked protein", which is a stepping stone when infecting cells with protrusions on the surface of the virus, are mutated.

● “93% in the UK and 72% in the US are“ BA.2 ””

The percentage of “BA.2” among the newly confirmed infected persons is

▽ In the UK, the health authorities will take a week until March 27, 2022. In


United States, the CDC = Centers for Disease Control and Prevention estimates that it is 72.2% in the week until April 2, 2022.

● “93% will be“ BA.2 ”in May in Japan” In

Japan, the National Institute of Infectious Diseases estimated the ratio of “BA.2” nationwide based on data from private testing companies. As of mid-March 2022, it was around 30%, but it is expected to account for 93% in the first week of May and 100% in the first week of June.

In "BA.1", a few weeks after the community-acquired infection was confirmed in late December 2021, in mid-January 2022, the Delta strain was almost replaced.

"BA.2" is not as rapid as when it was replaced with "BA.1" after a community-acquired infection was confirmed in Tokyo in mid-February, but it is being replaced.

Features 1. “Infectivity is stronger than“ BA.1 ”” WHO

WHO = World Health Organization states that "BA.2" is more infectious than the Omicron strain "BA.1", which was the mainstream in the 6th wave.

According to an analysis using Danish data, "time from one person's infection to another" = "generation time" is 15% shorter than "BA.1" and "one person spreads the infection to how many people" The "effective reproduction number" that indicates "ka" is said to be 26% higher.

Feature 2. Is the severity rate low?

The severity rate appears to be low, and WHO found that there was no difference in the risk of hospitalization between those infected with "BA.1" and those infected with "BA.2" as a result of analysis in the United Kingdom. ..

Feature 3. "BA.1" infection → "BA.2" infection

Even people infected with "BA.1" can be infected with "BA.2".

■ Effect of vaccine

According to the data compiled by researchers of the British health authorities, the effect of the vaccine was 71.3% for "BA.1" at ▽ 1 week

after the third inoculation , while "BA.2".

Was 72.2%, which did not change much.

On the other hand

, after 15 weeks or more, it dropped sharply to 45.5% for "BA.1" and 48.4% for "BA.2".

■ Increase in the number of infected people now “The replacement with“ BA.2 ”has a strong impact”

An expert meeting of the Ministry of Health, Labor and Welfare held on April 6, 2022 said, "It is thought that the increase in contact opportunities and the replacement with the'BA.2'strain have a strong influence on the current increase in the number of infected people. ".

Motoi Suzuki, director of the National Institute of Infectious Diseases Epidemiology Center for Infectious Diseases, said, "In the (next) 7th wave," BA.2 "is expected to be the main body. It is necessary to prepare a medical system considering the possibility that the wave will be higher than the 6th wave. "

When the Omicron strain "BA.1" began to spread in the 6th wave, it was found that it was less likely to become severe than the Delta strain, and it is thought that the sense of caution was diminished.

However, the number of infected people has increased significantly compared to the spread of the infection so far, and as a result, the number of people dying has increased.

I am worried that the same thing will happen in "BA.2".

■ With the progress of the third vaccination ...

On the other hand, what is different from January 2022, when the sixth wave started, is the progress of the third vaccination.

According to the government's announcement, as of April 11, about 85% of the elderly aged 65 and over in Japan have completed the third vaccination, and the total population is about 45%.

In particular, it is thought that the number of people who die will decrease as the third vaccination progresses in the elderly, and it may be possible to reduce the number of people who become severely ill or die.

In the summer of 2021, when the second vaccination actually proceeded, the effect of the vaccine reduced the number of elderly people dying, according to an expert meeting of the Ministry of Health, Labor and Welfare.

Atsuro Hamada, a specially appointed professor at Tokyo Medical University, who is familiar with the situation of infectious diseases overseas, said, "In most countries around the world, it has been replaced by the" BA.2 "strain, and in some countries it exceeds 90%. In Japan as well, it is important to take preventive measures a little stronger while reducing contact opportunities, and to promote additional vaccinations. Especially since the number of infected people in their 20s is increasing, measures for this generation May be the key to lightening the re-increase. "

■ New type "XE" confirmed for the first time in Japan

Furthermore, a type called "XE", which is a new mutant virus that combines multiple viruses, has been reported in the United Kingdom and other countries.

It was confirmed for the first time in quarantine in Japan.

1. "XE" confirmed for the first time in Japan A woman arriving in Narita is quarantined

The Ministry of Health, Labor and Welfare announced on April 11 that "XE" was confirmed for the first time in domestic quarantine.

The infection was confirmed in a woman in her thirties who entered the country from the United States. After arriving at Narita Airport on March 26, the test was positive at the quarantine station, and the results of analyzing the gene of the sample at the National Institute of Infectious Diseases. It means that it was confirmed as "XE".

2. "XE" ... "BA.1" + "BA.2"

Viruses acquire new properties by repeating small mutations, but apart from that, when one person infects multiple types, gene recombination occurs and a new virus that combines multiple viruses can be created. I have.

"XE" is a type made by combining multiple viruses, and the Omicron strains "BA.1" and "BA.2" are combined.

Most of the parts that are on the surface of the virus and contain spike proteins that serve as a foothold for infecting human cells are "BA.2" and the other parts are "BA.1".

3. "XE" infection spread speed "12.6% faster than" BA.2 ""

WHO classifies "XE" as a type of Omicron strain, and according to data from the UK health authorities, 1179 cases have been reported by April 5 since it was first reported in the UK on January 19, 2022. ..

Smaller clusters have also been reported, but less than 1% of all viruses analyzed.

As a result of analysis using a mathematical model based on the data up to March 30, it is estimated that the speed at which the infection of "XE" spreads is 12.6% faster than that of "BA.2".

■ Viruses that combine multiple viruses Other than that ...

There are other types of viruses that combine multiple viruses, of which "XD" and "XF" are called the Delta strain that spread in the "Fifth wave" last summer and the Omicron strain "BA.1". It is a combination of types.

1. "XD" ... Mostly Delta strain + Spike protein is "BA.1"

"XD" has a spiked protein part of "BA.1" and most of the others are Delta strains, and according to the data of the British health authorities, it was first detected on December 13, 2021. As of April 1, 2022, 66 cases were reported in France, 8 cases in Denmark, and 1 case in Belgium.

WHO positions "XD" as a mutant strain under surveillance, where the degree of influence on the infectivity, severity of infection, vaccine effect, etc. is not clear, but the spread of infection is limited. It is said that.

2. "XF" ... Partly Delta stock + Mostly "BA.1"

In addition, most of "XF" including spike protein is "BA.1" and some are delta strains.

Health officials in the United Kingdom have found 39 cases in the United Kingdom since January 7, 2022, but have not reported since February 14, and the spread of the infection has not been seen.

3. Check "BA.4" and "BA.5" ...

In addition, mutant viruses called "BA.4" and "BA.5", in which the spike protein gene is mutated in other types, have also been confirmed in South Africa and elsewhere.

The infectivity and severity of infection are not yet well understood.

WHO says that the risk of new mutant viruses being created by combining multiple viruses is still high, and it is still essential to analyze the genes of the virus and share the data.

Professor Hamada of Tokyo Medical University said, "" BA.4 "and" BA.5 "are one of the subtypes of the Omicron strain like" BA.2 ", and the process of infection and proliferation of one Omicron strain. It has emerged as a mutation in Tokyo. It is not yet known whether the infection will spread and become a threat, or if the infection will not spread so much, but it is very important to monitor it. Of these, "XE" is said to be highly infectious, but it is difficult to judge at this stage whether it will cause a major epidemic. Rather, we are wary of the possibility that a new mutant virus completely different from the Omicron strain will appear. It should be, and it is important to continue the monitoring system such as genome analysis. "

■ Expert "Basic daily measures do not change"

The current number of new infections continues to be higher than the peak of the fifth wave last summer.

An expert meeting of the Ministry of Health, Labor and Welfare said that there was further


about the possibility of rebound


We are calling for thorough measures such as

proper wearing of non-woven masks, disinfection, ventilation, and avoidance of congestion .

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, "It is not a virus with a mutation that was completely unexpected. It seems unlikely that "BA.2" is becoming the mainstream now, but even with the XE strain, the basic daily measures have not changed, and the policy of wanting the third vaccination to continue has changed. No, "he said.