For previously unknown reasons, children who received the measles vaccine were less likely to die from infectious diseases other than measles. According to Michael Mina, a postdoc in biology at Princeton University and a medical student at Emory University, the difference is significant. “In some developing countries, where infectious diseases are very high, the reduction in mortality has been up to 80 percent. So it’s really been a mystery – why do children stop dying at such high rates from all these different infections following introduction of the measles vaccine?”
Based on epidemiological data from countries before and after the measles vaccine was introduced, scientists believe they may have an explanation for this mystery that is part correlation and part causation. So what’s the difference (and why do we care)?
Correlation means that two or more events tend to occur about the same time and might be associated with each other, but aren’t necessarily connected by a cause-and-effect relationship. Causation means that a specific action causes a second event to happen. A cause-and-effect relationship results from causation. Sometimes it’s very difficult to distinguish between the two. This is where the importance of evidence comes in.
In this case, part of the decrease in death due to infectious diseases can be considered due to correlation. In this case, children who received the measles vaccine must have had access to healthcare, including the measles vaccine. If they received the measles vaccine, they were also likely to receive other vaccines and treatment for other infectious diseases, meaning their death rates from other diseases were also lower. The measles vaccine did not cause the reduction in deaths from infectious diseases, the access to healthcare did. Getting the measles vaccine also resulted from the same cause, access to healthcare.
In addition to this correlation, epidemiological data from several countries from prior to the introduction of the measles vaccine shows that the number of measles cases predicted the number of deaths from other infectious diseases two to three years later. Their hypothesis, supported by studies in monkeys, suggest that the measles virus actually erases immune protection to other diseases. So, if a child gets measles, he or she loses some of the immune system’s “memory” of how to fight diseases can also be wiped out. Preventing a child from getting the measles (by getting a measles vaccine) is believed to prevent deaths from other infectious diseases as well.
Although more testing is needed to verify the causation, scientists hope it will provide more evidence for parents to vaccinate their children. Epidemiologist William Moss, who studies the vaccine at John Hopkins University, says “The reduction in overall child mortality that follows measles vaccination is much greater than previously believed. I think this paper will provide additional evidence – if it’s needed – of the public health benefits of measles vaccine. That’s an important message in the U.S. right now and in countries continuing to see measles outbreaks.”
To view the cause-and-effect relationships (both correlation and causation) between the measles vaccine and decreased mortality from childhood infectious diseases, please click on “Download PDF” above. To learn more about the epidemiological study, click here.