At least 94 cases of the new coronavirus Omicron strain "BA.2" have been reported in Japan so far in a survey by the National Institute of Infectious Diseases.

It accounts for about 0.6% of all Omicron strains.

According to a genetic analysis of the new coronavirus conducted by the National Institute of Infectious Diseases, the virus of the Omicron strain "BA.2" was announced as of 16th this month from the end of last year to the 30th of last month. , 94 cases have been reported nationwide.



On the other hand, more than 16,000 cases of "BA.1" virus, which is currently the mainstream of the epidemic, were detected in the same period, and the ratio of "BA.2" to the total Omicron strain was about 0.6%. That is.



However, it is a tentative result because it may take time to report the gene analysis, and the ratio may differ from region to region.



The National Institute of Infectious Diseases will continue to monitor the trends of "BA.2" through genetic research.

Expert "It is necessary to strengthen monitoring sufficiently in the future"

Regarding the domestic situation of the Omicron strain "BA.2", Professor Atsuro Hamada of Tokyo Medical University, who is familiar with overseas infectious diseases, said, "As far as the survey results are concerned," BA.2 "in Japan at this point in time. It is considered that the situation is not widespread. There are no reports from overseas that "BA.2" has increased the number of seriously ill people or the vaccine has become less effective than "BA.1", so there is no change as a countermeasure. However, there are countries where "BA.2" spreads and countries where it does not, and the detailed reason why it is different is not yet known, and it is undeniable that the epidemic will be prolonged if it spreads in Japan. , It is necessary to strengthen the monitoring sufficiently in the future. "

Further research required "BA.2" may have stronger symptoms than "BA.1"

When a group such as the University of Tokyo experimented with a virus called "BA.2", which is a type of Omicron strain of the new coronavirus, using cultured cells, it showed symptoms compared to "BA.1", which is currently the mainstream. It turns out that the triggering force may be stronger.



This was published on the Internet by a group of Associate Professor Kei Sato of the Institute of Medical Science, the University of Tokyo, as a "preprinted paper" before being checked by a third party.



The group artificially created a virus that reproduced the characteristics of the spike protein of "BA.2", infected cultured cells, and investigated the reaction.



As a result, the virus that reproduced "BA.2" had a weaker ability to destroy surrounding cells when infected, but was 1.5 times higher than that of "BA.1". ..



Furthermore, in an experiment to infect hamsters, "BA.1" did not detect the virus in the lungs and did not lose weight, but in the virus that reproduced "BA.2", the virus was also confirmed in the lungs and the body weight was reduced. There was a tendency to do.



The group said that because of the experiment with the artificially created virus, further research is needed to find out what the actual symptoms will be, and "BA.2" causes stronger symptoms than "BA.1". There is a possibility.

Associate Professor Sato says, "Experiments suggest that'BA.2'has different characteristics. These two viruses may need to be dealt with as separate viruses."

Reported that there is no difference in hospitalization risk in overseas studies

In overseas studies such as Denmark, it has been reported that there is no difference in the risk of hospitalization between "BA.2" and "BA.1".



According to Associate Professor Kei Sato, reports on the risk of hospitalization from overseas are data on the progress of the third vaccination to a certain extent, and it is possible that the vaccine can prevent the disease from becoming more severe. Is that there is.



Since the results of this research are experiments on cultured cells and animals using an artificially reproduced virus, it is necessary to carefully judge what kind of symptoms actually occur in humans, but the characteristics of the virus itself. It is important to note that "BA.2" may cause more severe symptoms than "BA.1".