STAT news answers common questions about the science of the flu shot.

Can repeated vaccination actually backfire?

There’s been a growing belief that getting a flu shot year after year can impede the immune system’s ability to generate a strong response to the vaccine. It’s not thought that this phenomenon happens every year. But in some years when the viruses in the vaccine haven’t been updated but the viruses that are circulating are different from the vaccine version, people who have been repeatedly vaccinated may end up being more likely to get infected. Influenza researchers call this “negative interference.”

Dr. Danuta Skowronski of the British Columbia Center for Disease Control has published papers showing this effect. She said the research community’s consensus appears to be accepting that this is real.

Do I have to be worried about the statin factor when getting a flu shot?

There have been concerns that commonly used cholesterol-lowering drugs, statins, might actually undermine the effectiveness of flu vaccine. A couple of studies had raised questions about the possibility that the drugs might dampen the immune response triggered by vaccine. That was particularly worrying because the people who take statins — adults in late-middle age and older — are often the people who are at highest risk of becoming seriously ill or dying from influenza. (At least in H3N2 flu seasons; more on this later.)