Over 230 cases of highly infectious variant strains of the novel coronavirus have been confirmed in 19 of the 47 prefectures in Japan, government data showed Thursday, with health experts warning of a potential "fourth wave" of infections should they continue to spread across the country.The government is monitoring three mutant strains of the coronavirus originating from Britain, South Africa and Brazil. Following the first confirmed case of the new variants in Japan on Dec. 25, 234 have been reported as of Thursday, including those detected at airport quarantine.Saitama Prefecture account…READ FULL ARTICLE