All viruses change over time. The more people a virus infects, the more chances it has to mutate into a new variant. So countries in which the coronavirus is spreading more widely are more likely to see problems like this, experts say. The surest way to boost the chances of a worrisome coronavirus mutation: let it spread unchecked. “More infected people means more opportunity for the development of mutations. More movement of people … means new variants can spread faster,” Dr. Shira Doron, an infectious-disease specialist at Tufts Medical Centre, told Business Insider. When viruses infect a body, they replicate. More spread means more replication, which raises the likelihood of genetic errors. So in places where transmission is high, we are more likely to see a harmful variant emerge, experts say.