Among the Omicron strains of the new coronavirus, a mutant virus of the type "BA.5" has become mainstream in Europe and the United States and is spreading in Japan as well.



Experts said, "The infectivity is a little strong, and some people with immunity may be affected, so it is inevitable that the number of infected people will increase to some extent. If the number of infected people increases, some people will become seriously ill. It will come out, so we need to be careful. "

What is "BA.5"?

"BA.5" is a type of Omicron strain, which was confirmed in South Africa in February, and has spread mainly in Europe and the United States since May. According to WHO = World Health Organization, it was detected worldwide in the middle of last month. It accounts for about 40% of all new coronaviruses.



In the United States, it accounts for more than half of the total in the week leading up to the beginning of this month, and is thought to be contributing to the recent increase in infection.



According to a statement released by the British health authorities on the 24th of last month, "BA.5" is expected to spread 35.1% faster than the previously mainstream "BA.2".



According to a report at the monitoring meeting in Tokyo, 25.1% of the cases were suspected of being "BA.5" in the week leading up to the 20th of last month.

feature is

"BA.5" is a protrusion on the surface of the virus, and mutations such as "L452R" have occurred in the "spiked protein" that serves as a foothold when infecting cells, and it has the property of escaping immunity. "BA.5" means that there is an experimental result that the effect of the neutralizing antibody that suppresses the action of the virus is less than one-seventh that of the "BA.1" of the Omicron strain that initially spread.



In addition, it is thought that the immunity obtained by vaccination and infection is weakening over time, which also contributes to the spread of infection.



According to materials presented by Professor Hiroshi Nishiura of Kyoto University at an expert meeting of the Ministry of Health, Labor and Welfare held on the 30th of last month, the proportion of people with immunity to the Omicron strain has begun to decline in all age groups, and as of the end of June. It is 44.6% for those in their 20s and 37.4% for those in their 70s and above.

Severe

On the other hand, WHO stated in a weekly report on the 22nd of last month that "there is no information that it has changed compared to'BA.1'" as to whether it is likely to become severe if infected, and ECDC = European Centers for Disease Control and Prevention also In a report on the 13th of last month, the data are still limited and "there is no evidence of increased severity."



However, he points out that as the number of infected people increases, the number of hospitalizations and deaths may increase.



In addition, UK health officials analyzed data on vaccines from people infected during the month or so until late May, and found that people infected with "BA.5" and those infected with "BA.2". Reported that there was no significant difference in the effectiveness of the vaccine.

Atsuro Hamada, a specially appointed professor at Tokyo Medical University who is familiar with overseas infectious diseases, said, "The infectivity is a little stronger than the type of Omicron strain that has been prevalent until now, and some people with immunity may be affected. In addition to replacing "BA.2", it is inevitable that the number of infected people will increase to some extent. According to reports from each country, the severity of infection has not changed much so far, and it is about the same as the conventional Omicron strain. However, if the number of infected people increases, some people will become seriously ill, so we need to be careful. "