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Frenemies: Chronic cytomegalovirus infection boosts flu vaccination efficacy (IF you’re young)

cheapo boost"The enemy of my enemy is my friend." This phrase, or at least the thinking it embodies, is at least 2,400 years old. So, there must be something to it, right?

Of course, it's arguably a vast oversimplification. The more nuanced and much newer term "frenemy," dating back merely to the early 1950s, is more apt in the case of infection by the microbe known as cytomegalovirus (CMV, for short). If the name is unfamiliar, brace yourself: You've probably already been introduced. It's ubiquitous.

"Between 50 percent and 80 percent of adults in the United States have had a CMV infection by age 40," states a page on the National Institutes of Health's website. (Worldwide, the proportion of people infection exceeds 90 percent.) Once CMV is in a person's body, it stays there for life," the page soberly adds.

For the most part in healthy people, CMV pretty much sits there inside of cells (particularly in the salivary glands), pretty much biding its time and getting slapped down by the immune system if it tries to act up.

On the other hand, the virus can cause serious trouble if you're immune-compromised: say, getting a bunch of immune-suppressing drugs pending or after a transplantation operation, or carrying another virus, the infamous immune-deficiency-causing HIV (which as far as we know is nothing but an enemy, plain and simple.)

But in a new study published in Science Translational Medicine, Stanford immunology expert Mark Davis, PhD, and his colleagues show that carriers of CMV mount a more robust immune response to seasonal influenza vaccinations, increasing the chances that the annual vaccine will be more effective in those people.

That's the good news. The not-so-great news is that this only holds for young people (20-30 years old), not the older ones (age 60 and up) who could really use a boost: The older you get, it's well known, the less effective the standard seasonal flu vaccine is in helping you fight off an influenza infection.

Experimenting with mice, Davis and his associates went a step farther. They actually infected the animals with influenza itself. Sure enough, young mice who were carrying CMV fought off the bug better than the non-infected mice did.

That's the good news. The not-so-great news is that the old mice didn't.

And although the study didn't say so, one wonders whether in young people whose immune systems are going strong, that extra rocket fuel CMV seems to provide may have a dark side, for example a tendency to autoimmunity. Women's immune systems tend to be more robust than those of men (very possibly due to the effects of testosterone, as Davis and his crew found a little over a year ago. And they have several times the rate of many autoimmune diseases that men do.

Previously: In human defenses against disease, environment beats heredity, study of twins shows, Why do flu shots work in some but not others? Stanford researchers are trying to find out, In men, a high testosterone count can mean a low immune response and Mice to men: Immunological research vaults into the 21st century
Photo by Joe Lillibridge

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