Study: Flu Shots May Slow Virus Changes

Flu viruses change as they pass back and forth between people who have been exposed to the virus and those who had not been exposed before, new research suggests. People are exposed by getting infected or vaccinated. Researchers say vaccinating more people who have not been exposed — especially children — may slow the process of change. The study looked at changes in an H1N1 virus, an older strain that is similar to the current H1N1 (swine) flu. Researchers injected virus into several groups of mice. Some had been vaccinated. Some had not. In the vaccinated mice, the virus changed into a form that clung tighter to cells. This helped the virus to fight off antibodies in the immune system. But it also meant the virus did not spread as easily. In the unvaccinated mice, the virus spread and multiplied easily. It didn’t change much.