Sunday marked two years since the World Health Organization declared a public health emergency of international concern due to the outbreak of the novel coronavirus.
While the omicron variant has been raging at home and abroad, a variant of the variant, called BA.2, has begun to spread, prompting the WHO to intensify surveillance.
BA.2 was detected in Africa around November last year and spread to Europe and Asia. In Denmark, the variant has become more prevalent than the mainstream omicron BA.1. In England, 1,072 cases of BA.2 had been confirmed as of Jan. 24.
In Japan, BA.1 accounts for the majority of cases but, according to the Health, Labor and Welfare Ministry, BA.2 has been detected in 313 people in quarantine as of Wednesday. Many of the cases are said to be found in people traveling from India and the Philippines. Reports of the variant have begun to emerge within Japan, too, such as the detection of BA.2 in two people in Kobe confirmed to be infected between Jan. 10-16.
BA.1 has about 30 mutations in the virus' surface protrusions, sharing many with BA.2 that affect infectivity and vaccine efficacy. However, BA.2 lacks 10 mutations found in BA.1 and has six mutations not found in BA.1.
A Kyoto University analysis found that the effective reproduction number, which indicates the number of secondary cases an infected person causes, is 18% higher than in BA.1. Researchers in Britain also found it to be slightly more infectious.
The National Institute of Infectious Diseases said the difference in hospitalization rates between BA.1 and BA.2 is "not clear."
"BA.2 has many mutations, so it's difficult to predict the impact of its spread," said Tetsuya Mizutani, a professor of virology at Tokyo University of Agriculture and Technology.
British health authorities announced Friday that the effectiveness of a vaccine in preventing the onset of disease two weeks after a third dose was 63% for BA.1 and 70% for BA.2.
It is believed that there is no significant difference regarding the aspect of a vaccine's efficacy for the two variants.
"A third shot may be effective to some extent with BA.2," said Retsu Fujita, an associate professor of infectious disease epidemiology at the International University of Health and Welfare
Some tests conducted overseas showed that BA.2 is a delta variant, so it was also called "stealth omicron." In Japan, tests done at universities and local public health institutes showed that BA.2 is an omicron variant.
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