USA TODAY The virus that causes COVID-19 changes all the time. In most cases, the changes are harmless. But they can add up. And when they do, the virus can become more contagious or deadlier, and potentially evade vaccines, treatment, diagnostics or natural immunity. We know that a number of these potentially more dangerous or difficult variants are circulating in the U.S. in increasing numbers. But scientific leaders say there's no reason to panic about the variants yet. Instead, what needs to happen is more research into the potential risks of these variants, better tracking of these changes and a doubling down on protection efforts that we know work, including wearing face masks, avoiding crowds, and getting vaccinated as soon as possible.