A research article published in the journal Science attempted to determine how the Measles virus (MV) impacts child mortality from other infections 2-3 years after a Measles infection. The scientists used population-level data from the UK and the USA starting from the time of mass measles vaccinations. They illustrated a positive correlation between MV infection and mortality from unrelated infections. Although the MV virus activates the immune system, it also suppresses it in such a way that weakens the body, making it more vulnerable to other pathogens that would have been removed by the immune system if not for the MV infection.
Earlier this year, there was a multi-state outbreak of the Measles virus (MV). The CDC believes that the likely cause was a traveler who acquired the virus overseas and while infectious, he/she visited an amusement park in California. This was the perfect place for the virus to spread because unvaccinated children are at the highest risk. Measles is extremely contagious and in children, can cause serious side effects (eg. pneumonia, lifelong brain damage, deafness, death). The measles-mumps-rubella (MMR) shot provides efficient protection against measles; however, due to religious reasons or unfounded mistrust of this safe vaccine, children remain unvaccinated, which exposes them to this deadly virus.
It is likely that the traveler was unaware of his/her infectivity status because symptoms do not appear until ten to twelve days post infection and can last up to a week. Measles causes robust immune suppression, which can last between several weeks and months after the initial stages of the infection. For this reason, most deaths caused by measles are due to secondary infections. MV is also observed to activate the immune system, known as the “paradox of measles”. A research group in 2012 studied MV infection in Macaques in an attempt to explain this paradox.
Memory immune cells are important for remembering the tools that must be employed if infectious agents are encountered again. The 2012 Macaques project indicated that these cells are eliminated during MV infection, resulting in a “temporary immunological amnesia”. Restoration can take several weeks or months (or even years according to the Science article). During this recovery period patients are susceptible to infections they previously possessed immunity to (ex. chickenpox). Co-author of the article published in Science stated, “…if you get measles, three years down the road, you could die from something that you would not die from had you not been infected with measles."
The researchers propose that this “temporary immunological amnesia” after measles infection should be detectable through epidemiological data.
- They used population-level data to determine the relationship between measles infections and suppressed immune systems
- They analyzed epidemiological data for children in the UK and USA ages 1 through 9 and 1 to 14, respectively, after the initiation of mass vaccination in each country.
The data collected clearly shows that the measles infection had a 2 to 3-year impact on mortality from other infectious diseases. Co-author Grenfell states, "In other words, reducing measles incidence appears to cause a drop in deaths from other infectious diseases due to indirect effects of measles infection on the human immune system…At the population level, the data suggests that when measles was rampant, it may have led to a reduction in herd immunity against other infectious diseases."
They conducted a similar analysis with pertussis or whooping cough, another vaccine-preventable disease, but not known to be immunosuppressive. In this examination, they observed no correlation between pertussis infection and mortality from other infectious diseases. This illustrates that MV, unlike pertussis, affects children’s protection against other diseases. Michael Mina, the lead author of the article, states "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.”
Being able to induce “immunological amnesia” can be beneficial in terms of autoimmune disorders and allergies. In both cases, the immune cells are attacking antigens that are not dangerous, and such attacks can be deadly. By fully understanding the mechanism employed by MV, researchers could create a drug that selectively destroys immune cells that are harmful to the body.
Measles Cases and Outbreaks. Retrieved from http://www.cdc.gov/measles/cases-outbreaks.html
Measles and the Vaccine (Shot) to Prevent It. Retrieved from http://www.cdc.gov/vaccines/vpd-vac/measles/fs-parents.html
Measles. Retrieved from http://www.who.int/mediacentre/factsheets/fs286/en/
De Vries, R.D., McQuaid, S., van Amerongen, G., Yuksel, S., Verburgh, R.J., Osterhaus, A.D.M.E., Duprex, W.P., & de Swart, R.L. (2012). Measles Immune Suppression: Lessons from the Macaque Model. PLOS Pathogens.Retrieved from http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1002885
(2015). Long-Term Measles-Induced Immunomodulation Increases Overall Childhood Infectious Disease Mortality. Science,348(6235), pp. 694-699. Retrieved from http://www.sciencemag.org/content/348/6235/694.full.pdf
Grenfell, B. & Metcalf, J. (2015). Long-Term Measles-Induced Immunomodulation Increases Overall Childhood Infectious Disease Mortality. http://wws.princeton.edu/faculty-research/research/item/long-term-measles-induced-immunomodulation-increases-overall