The World Health Organization (WHO) has now classified a coronavirus variant first documented in Colombia in January as a “variant of interest.”

The “Mu” variant—officially named B.1.621—was designated a “variant of interest” on Tuesday. It joins the previously designated variants of interest Eta, Iota, Kappa, and Lambda. According to WHO, Mu received the designation because it has “some mutations that need to be studied for their potential impact on the body’s immune response.”

Additionally, data shared with the WHO Virus Evolution Working Group indicated that “immunity developed through prior infection or vaccination may not be as strong against this variant.” However, more studies are needed to verify this.

WHO added that circulation of this variant has been on the decline worldwide, though its pervasiveness in Colombia and Ecuador has been increasing as of late. Moving forward, WHO told Complex, the variant’s epidemiological evolution will be closely monitored. Studies, as mentioned above, will also be carried out.