Photo/Illutration The Gunma prefectural government office building in Maebashi, Gunma Prefecture (Asahi Shimbun file photo)

Twenty-six more workers at a factory in Ota, Gunma Prefecture, have tested positive for COVID-19 in a continuing cluster outbreak as prefectural officials reported 30 new cases on Dec. 5. 

That brought the total number of people infected at the factory, located 100 kilometers north of Tokyo, to 42. 

They include both males and females and range in age from the teens to the 50s. Although the Delta variant was detected in two samples extracted from people who contracted the virus at the factory, prefectural officials believe that it is unlikely that anyone has been infected with the Omicron strain.

None of the patients are reported to be seriously ill. All either have a mild condition or are asymptomatic.

Prefectural officials say they still don’t know why the cluster broke out and spread in the factory. They report that 29 of the 42 people infected had a second dose of a COVID-19 vaccine within the past four months.

The factory has had 91 employees take a polymerase chain reaction (PCR) test so far, with another 300 expected to undergo testing in the days ahead.