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We health professionals tend to be rather jaded about the value of natural products. We know all too well that naturally occurring entities are not necessarily healthy. Water is natural and essential for life, but it can be toxic value if consumed in massive quantities. Unadulterated mercury is good for thermometers but not for the human brain. And artificial-free tetrodotoxin is useful for pufferfish but not for dinner.
And then there is natural immunity. Earlier this year, we heard quite a bit about this in the context of our nation's measles outbreak, which was linked to substandard vaccination rates and international visitors to Disneyland. Some in the anti-vaxx movement took the outbreak as an opportunity to espouse the supposed benefits of natural immunity over vaccine-induced immunity, saying that which does not kill us makes us stronger. But we intuitively know that this concept is misdirected and irresponsible. Thanks to a recent study published in Science, our intuition is now supported by peer-reviewed data.
The study, “Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality,” was inspired by author Michael Mina's earlier primate research. (2015;348:694.) Mr. Mina is a medical student at Emory University, and collaborated with researchers at Princeton and the department of viroscience at Erasmus University, Netherlands.
His primate research, done at Erasmus, found associations between the measles infection and subsequent immune memory-cell depletion. These studies demonstrated that measles attacks B and T lymphocytes, and that even though peripheral blood lymphocytes rebound to normal levels within a few weeks, the new cells are mostly measles specific: good at detecting and fighting measles but not so good at remembering and fighting other infectious agents. Recall that starting around age 6 months, antibodies from an infant's mother start to wear off and the child has to forge his own immune system one exposure at a time. The implication is that after the measles infection, the immune system becomes less effective at fighting previously encountered diseases.
Min et al. investigated whether such immune amnesia might also be present in human populations by looking at childhood deaths between ages 1 and 9 in the UK and Denmark and 1 and 14 in the United States, in both pre- and post-vaccine eras. They looked quite broadly at all infection types, and attempted to focus on infections (like strep) that were acute, not vaccine-preventable at the time of the study, and common enough in the community that most subjects would likely have had some prior immune exposure. Their outcome measure excluded measles infections as well as those from specific types of trauma (like animal bites) and from acute events (like food poisoning.) Their unadjusted scatter plots of measles incidence versus death from other infectious diseases uncovered a very strong correlation that included a 28-month lag period. These findings were consistent in all age groups across the three nations studied and in the pre- and post-vaccine eras. Extensive modeling, as detailed in the 41-page manuscript supplement, adjusted for time trends and confounders, and confirmed this link between the measles infection and risk for infectious disease death from other causes for up to 28 months after measles infection.
With these results in mind, let's come back to the question of natural immunity as being naturally better. We've all heard arguments from vaccine skeptics that kids should get their measles immunity naturally and that their “wild” immunity will be better than vaccine immunity. It's true in one way; having and recovering from measles is better protection against future measles disease than being vaccinated against it, just like having and recovering from Ebola is protective against future Ebola infection. Vaccine skeptics may be right about the protection against measles afforded by natural immunity, but they are wrong (based on this study) about immunity against virtually everything else. Even if a parent is willing to take the risk that his child might die from measles or be disabled by encephalitis, results from Mina et al. strongly suggest that overall immunity is depleted for more than two years after measles infection. That which does not kill us makes us weaker in this case.
Bottom-line, to quote Mina: “Our findings suggest that measles vaccines have benefits that extend beyond just protecting against measles itself. ... It is one of the most cost-effective interventions for global health.”
Naturally, I agree.
You can learn more about this topic by listening to the Medically Clear podcast on iTunes or on Dr. Ballard's website,http://dballard30.podbean.com.Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.