New Study Finds: Just Five Percent of Unvaccinated Children Can Cause a Measles Epidemic

Measles is the most contagious viral disease in the world. Additionally, it can have serious consequences: about twenty percent of those infected may suffer complications such as pneumonia, encephalitis, and later even deafness or retardation. Death from the disease is not an uncommon outcome. Until 1980, when the vaccine became routine, measles was responsible for the death of approximately 2.6 million people worldwide each year.

In recent decades, most of us haven't really feared measles, against which babies and children are routinely vaccinated. However, a new American study found that there is indeed reason to worry. Even a small minority that stops vaccinating, they say, significantly raises the risk of contracting the disease.

Using computer models, researchers from Stanford University's School of Medicine and Baylor College found that a five percent drop in measles vaccination among children aged two to eleven would triple the annual number of measles cases in this age group, leading to additional health expenses exceeding two million dollars.

"We focused on measles as an example of the harm from declining vaccine coverage because it is a highly contagious disease," explained Nathan Lo, the lead researcher. "This is likely the first contagious disease to break out if vaccination rates continue to decline."

To prevent a measles outbreak, at least 90-95 percent of the population needs to be vaccinated, creating what is known as 'herd immunity.' Since there will always be infants too young to receive the vaccine, children and adults who cannot be vaccinated (due to an immune deficiency or allergy) as well as the few cases where the body doesn’t develop an immune response despite vaccination, general population immunization is necessary to protect those individuals.

Several states in the United States, the researchers say, are already close to falling below the threshold needed for herd immunity. According to the computer model, this is sufficient to create conditions for a significant measles outbreak. "I think our research is a wake-up call for what we can expect in the coming months and years as vaccination rates continue to drop in the 18 states that allow non-medical philosophical exemptions," the researchers state.

In Israel, of course, every parent is allowed not to vaccinate their child without needing to provide any justification. However, as this latest study illustrates, the more parents who choose to exercise this right, the greater the likelihood that measles epidemics will make a comeback and once again spread fear among us.