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Omicron subvariants BA.4, BA.5 confirmed for 1st time in Japan at airport quarantine

The central government building housing the Ministry of Health, Labor and Welfare is seen in Tokyo's Chiyoda Ward. (Mainichi/Kimi Takeuchi)

TOKYO -- A total of three people infected with the BA.4 and BA.5 subvariants of the coronavirus's omicron strain have been confirmed at airport quarantine in Japan, the health ministry announced on May 12, the first time their existence has been confirmed in the country.

    These strains had previously been detected mainly in South Africa, Europe, and the United States, and are more likely to spread than the BA.2 subvariant that is currently the mainstream in Japan.

    BA. 4 was detected in a man in his 50s who arrived from South Africa on April 22, and BA. 5 was found in two men in their 60s who arrived from Spain and Zambia, respectively, on April 29. All three were asymptomatic at the time of arrival.

    As for the omicron variant, BA.1, which sparked the sixth wave of coronavirus infections, and BA.2, which is now the mainstream, have been confirmed in Japan.

    Hiroshi Nishiura, a professor of theoretical epidemiology at Kyoto University, presented data on the "effective reproduction number," which indicates how many people one person can spread the infection to, at a Ministry of Health, Labor and Welfare advisory board meeting on April 20. According to this data, in South Africa, the effective reproduction number was found to be 1.49 times higher for BA.4 than for BA.1 and 1.4 times higher for BA.5 than for BA.1, and the spread of these subvariants is proceeding in that country.

    (Japanese original by Sooryeon Kim, Lifestyle and Medical News Department)

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