Explaining Measles Outbreaks Despite High Vaccination Status
Last week, the CDC released the 2012 National and State NIS Data for Children, for ages 19 to 35 months. The report indicated that 90% of children in the U.S. are fully immunized for measles, mumps and rubella (MMR); polio; Hepatitis B and varicella. Additionally while only 0.8% of children surveyed were completely unvaccinated, the economic disparities that often accompany vaccine uptake have seem to narrow compared to what we’ve seen in the past.
Dr. Anne Schuchat, who directs the National Center for Immunization and Respiratory Diseases at the CDC emphasized that
“These are really good results. We’ve come a long way in the 20 years since the Vaccines for Children program was established,”
And she explains,
“A provider or clinician recommendation is the strongest influence on what parents do,” Schuchat said.
So while we applaud the immunization successes we are seeing and the providers who continue to educate their patients about the benefits of vaccines, some still wonder why we are seeing so many outbreaks of vaccine preventable diseases, especially measles. In exploring this concern it’s important to note a couple of concerning trends.
The first is that those who choose not to vaccinate often cluster together. For instance, there have been three significant measles outbreaks that have been responsible for the majority of the 159 cases so far this year; 58 cases were from New York City, 23 from North Carolina, and 20 from Texas. When looking at a complete rundown of the cases, it’s clear that many are a result of unvaccinated individuals who return to the U.S. after traveling to another country and contracting measles there. What we’re seeing is that about 82% of these cases involved people who were unvaccinated (82%) and another 9% who had unknown immunization status.
In Texas, for instance, the outbreak began with an unvaccinated individual who traveled overseas and returned unknowingly infected with measles. After this person attended church services, the disease began spreading among a church congregation that was often advised against vaccination by their very own pastor.
Another concern to address is the rising number of personal belief vaccine exemptions being filed in various schools across the country. Like minded people tend to flock together and nothing exemplifies this better than the pockets of unvaccinated children in certain schools. For instance, there is a fast-growing charter school in the Sacramento area of California that tends to cater to families from the former Soviet Union. Since many of these parents distrust vaccines, about 58% of kindergartners at the school have personal belief exemptions on file. Another 8% of the children in this school have medical exemptions, which may suggest that their health could be compromised if they were to suffer with symptoms of a vaccine preventable disease.
In schools with such drastically low immunization rates, public health officials worry that an outbreak of disease could have serious consequences to the health of those children who either didn’t confer immunity after receiving the recommended vaccines, are medically unable to be vaccinated or who are purposely unvaccinated. To a public health official, these schools are like ticking time-bombs. Yet, we continually hear parents of who choose not to vaccinated their child questioning how an unvaccinated child could be a risk to a vaccinated child.
“Aren’t your child’s vaccines supposed to protect him? What are you worried about then?”
While an unvaccinated child is 35 times more likely to contract measles as compared to a vaccinated child, as long as the disease is circulating it remains a threat to everyone. We must acknowledge that vaccines are not 100% effective, 100% of the time, which explains why parents of vaccinated children are still concerned about their children contracting a disease, especially if they are surrounded by others who are unvaccinated.
Let’s take the measles vaccine for example. It’s one of the most effective vaccines we have,. Only about 2 to 5% of people do not respond to their first dose of measles vaccine. And remarkably, after two doses of measles vaccine more than 99% of people develop immunity to measles. This is almost perfect, but still, not a 100% guarantee.
With every vaccine there is an issue of efficacy. In the case of measles, a person may not confer immunity with the first dose. The second dose of measles vaccine was not added to the recommended schedule until 1985, which means that people born before 1985 may be completely unaware of the benefit of a second dose, and therefore may remain under-immunized. Then, one day, when they decide to take a vacation to a place like England, that is experiencing a measles epidemic, they have just increased their chances of exposure and subsequent illness, despite the fact that they are vaccinated.
Additionally, there will always be a segment of the population who can’t be vaccinated. Either they have a medical issue that prevents vaccination, or they are too young to be fully vaccinated. In the case of measles, research indicates that infants acquire passive immunity from their mothers during pregnancy and breastfeeding. However, since these maternal antibodies may interfere with vaccine induced immunity, the first dose of measles vaccine is delayed until the child is 12 months of age. Of course, the timing of all this is extremely complex and it’s quite possible that the passive immunity can wane in some infants before the vaccine is received, leaving an infant exposed to disease at a time when they are at greatest risk for complications.
The measles outbreaks we are witnessing today help illustrate how a highly vaccinated population is still susceptible to disease outbreaks as a result of less-than-ideal vaccination coverage and inadequate immunity levels. While we are grateful that 90% of children are being vaccinated, we must remain vigilant in addressing the pockets of unvaccinated people who can easily serve as a reservoir for a variety of diseases that are preventable, yet still exist. In the past, we’ve relied on providers to help educate parents and state legislatures to control school vaccination exemption policies. But the time has come for concerned parents to play a vital role as well, as we work to counter the enormous amount of misinformation that continues to circulate in internet chat rooms and social media forums.