The new coronavirus variants have raised concerns about whether vaccines will remain effective against this disease. But the vaccines themselves could drive the evolution of more mutants. The virus is always mutating. And if one happens to produce a mutation that makes it less vulnerable to the vaccine, that virus could simply multiply in a vaccinated individual. But even if that happens, that's only one step in the process. If the vaccine keeps virus levels low, even mutated viruses, the infected person won't produce enough to spread to other people. Unfortunately, at the moment, scientists can't answer the most basic questions about this process. How much does the virus actually replicate inside a person who has been vaccinated with either one dose or two? And how effective is that vaccine at limiting infection enough so that the virus levels stay low and prevent the spread to other people? Andrew Read at Penn State University says, whatever the answers may be, vaccine resistance or escape, as it's called, isn't nearly as scary as bacteria becoming resistant to antibiotics. And this evolutionary pressure is present for any vaccine that doesn't completely block infection. Many vaccines, apparently, including the COVID vaccines, do not completely prevent a virus from multiplying inside someone even though these vaccines do prevent serious illness.