The team made up of researchers from the Tokai University School of Medicine based in Isehara, Kanagawa Prefecture, Osaka Kawasaki Rehabilitation University in Kaizuka, Osaka Prefecture, and the National Institute of Technology, Wakayama College in Wakayama Prefecture's Gobo announced the finding during a June 1 news conference at Minabe Town Hall in Wakayama. The group launched the research in October 2020 after being commissioned by the town of Minabe. The researchers compared viral reproduction in cultured cell samples, with one set treated with just coronavirus particles, and another with coronavirus mixed with umeboshi extract. They also changed extract concentration levels when studying the umeboshi-infused samples. They found that viral reproduction was suppressed in the cell samples with umeboshi extract, and the higher the extract concentration, the greater the effect. The group also claims that in addition to the coronavirus's original strain, the same result was confirmed for the alpha, delta and omicron variants. The team now plans to move to identify the reproduction-inhibiting ingredient.