Cytomegalovirus (CMV) causes much of the decay of our immune system over the years by cluttering it up with uselessly specialized anti-CMV cells. Via EurekAlert!: "results of a trial involving 441 CMV-negative women give rise to optimism that a vaccine to prevent congenital CMV may be closer. Women who received the trial vaccine were 50 percent less likely to later become infected with CMV ... Aspects of CMV biology have caused skeptics to question whether it is possible to prevent infection through vaccination, explains ... The virus is well adapted to persist in an infected person and is readily passed from person to person through direct contact with numerous bodily fluids ... Healthy people typically experience no symptoms after being infected with CMV. There is a strong immune response to the initial infection, but this immunity cannot always prevent subsequent infections if a person re-encounters the virus. Finally, natural infection does not elicit a response sufficient to completely eliminate the virus. On the contrary, once a person is infected, the virus persists for life." A vaccine is a start, but it doesn't help those of us already damaged by exposure: some methodology must be developed to remove specialized immune cells and restore function rather than just prevent loss.