evidence: The Unvaccinated Are a Risk to All of Us [...] The number of unvaccinated Americans is certainly a major public health concern. According to the Centers for Disease Control and Prevention, about 25% of U.S. adults are still unvaccinated, and many are clustered in regions where inoculation rates are especially low. Those clusters can easily become hot spots because they give the virus so many vulnerable hosts to attack. Indeed, that’s what we’ve seen recently as cases skyrocketed in especially undervaccinated states like Louisiana and Arkansas. [...] "Large numbers of unvaccinated people do make variants more likely," he says.