Courtesy: Reginald Mathalone/NurPhoto/Shutterstock (CNN) — The Delta variant is on its way to becoming the dominant strain of coronavirus in the US, raising concerns that outbreaks could hit unvaccinated people this fall. And a new study shows the Delta variant is associated with almost double the risk of hospitalization compared to the Alpha variant. The Alpha (B.1.1.7) variant, which is "stickier" and more contagious than the original strain of novel coronavirus, became the dominant strain in the US this spring. But health experts worry the Alpha variant could be trumped by the Delta variant, which appears to be even more transmissible and may cause more severe illness for those not vaccinated.