By MARIA CHENG
AP Medical Writer
The mu variant of the coronavirus was first identified in Colombia in January and has since caused isolated outbreaks in South America, Europe and the United States. The World Health Organization last month listed it as a “variant of interest” because of concerns it may make vaccines and treatments less effective, though more evidence is needed. So far, the mu variant doesn’t seem to be spreading quickly. Most countries remain concerned about the highly contagious delta variant; it is the dominant variant in almost all of the 174 countries where it’s been detected.