Alison M. Buttenheim, PhD, MBA, assistant professor at Penn Nursing answers parents' questions about childhood vaccines. Dr. Buttenheim is a public health researcher and social demographer who studies parent behavior and child health.

Q: What are vaccine refusal and delay?

A: Some parents decide not to have their children receive one or more of the vaccines recommended by the Centers for Disease Control, the American Academy of Pediatrics, and the Advisory Committee on Immunization Practices. Other parents choose to delay one or more vaccines. For example, if a child is scheduled to receive three shots at age two months, a parent might delay one of those shots for a few weeks or months. While some parents do this out of concern that too many needles at once may be traumatic for the child, research shows the unpleasant experience for the child is from the overall experience of getting shots, and not the specific number of shots given: Spreading out shots over several visits is actually more upsetting for most children.

Q: Are vaccine refusal and delay legal?

A: Each state has a required immunization schedule for entry into day care and school settings. Each state can also determine the process by which parents may claim an exemption from the schedule for their children. All states have provisions for medical exemptions, for example if the child has a specific immune disorder or an allergy that may make the vaccine unsafe for that child. Many states also have provisions for religious, philosophical, or personal belief exemptions, although the requirements to obtain these exemptions vary considerably from state to state. If a parent obtains an exemption according to state law, then the child may legally enroll in and attend day care or school.

Q: What prompts parents to refuse or delay vaccines for their children?

A: There has been a lot of research recently to try to understand parents' hesitancy around vaccines. One reason that has received a lot of media coverage is the unfounded idea that vaccines cause autism or other developmental or neurological conditions. This idea was first promoted in the late 1990s by a British doctor whose research has since been thoroughly discredited by the scientific community. Several rigorous scientific studies conducted since then have demonstrated that there is no link between vaccines and autism. However, this idea really persists in the minds of parents.

There are two other reasons for refusals or delays that we've heard in our research talking to parents. The first is the concern that the immunization schedule contains too many vaccines, which parents worry may overtax a child's immune system. Fortunately, this is not correct. The immunological challenge presented by the entire vaccination schedule is tiny compared to what a baby might encounter just crawling around on a floor or going on a trip to the supermarket. A baby's immune system is wonderfully designed to respond to these challenges, whether from bacteria on a toy or from the components of a vaccine.

The second reason we hear for opting out of the regular immunization schedule is the assumption that the diseases prevented by vaccines aren't common or dangerous. This tells us how successful the immunization program has been over the past decades: Most of us have never seen a case of measles or pertussis (whooping cough), and don't realize how dangerous these diseases can be, especially for young children. Unfortunately, due in part to parents not vaccinating their children, these disease are resurging in the U.S. We've seen recent outbreaks of measles in California and Minnesota, and California has had more pertussis cases in the past two years than they've seen in the last half-century. Parents should keep in mind that the reason they don't have to worry about these diseases is that the vaccines have been so successful in preventing them. But in order to maintain that level of protection, we need to make sure the vast majority of kids do get vaccinated. Children who can't get vaccinated are relying on the protection provided when everyone else is vaccinated an important concept called "herd immunity."

Q: If vaccinated children are in school with unvaccinated children, what are the possible adverse outcomes?

A: The adverse outcome we all want to avoid is an outbreak of a vaccine-preventable disease. Vaccines are very effective, but they are not 100 percent effective, so there is still a slight chance that a fully vaccinated child could contract a disease like measles if she were exposed to someone else with the disease. This could happen in any setting, but it's a particular concern if there is a large group of unvaccinated children in one classroom or one school. That gives a virus like measles a much better chance of finding a "susceptible" person - someone who can contract the disease and then pass it on to other people. So it's the clustering of unvaccinated kids in spatial or social groups like classrooms that we have to pay particular attention to.

Q: If parents of vaccinated children are concerned about their kids being in school with unvaccinated children, what can those parents do?

A: The easiest and most important thing to do is to make sure your child is up-to-date on all the recommended immunizations. Your pediatrician is very familiar with the vaccination schedule and will work with you to make sure your child is covered. You can learn more about the schedule from the CDC and from other reputable, credible sources like the Vaccine Education Center of the Children's Hospital of Philadelphia. When we talk to parents, they often say they are looking for information about vaccines presented in a straightforward, unbiased way. Both of these sites do a great job of that. They have lots of information about the science of vaccines, including how U.S. vaccine safety systems work, and can address concerns you might have about the vaccine schedule.

Another thing you can do is find out how many unvaccinated children are in your child's class or school. Sometimes this is as easy as asking the teacher or principal. Some states make that information available through their public health departments. What we know from our research in California is that the level of personal belief exemptions in an entering kindergarten class is usually higher in some types of schools than in other types of schools. For example, we know that Waldorf Schools in California have higher rates of exemptions compared to other schools. Parents who are worried about the presence of unvaccinated children in a school could start a conversation with the principal or PTA leadership to see how the issue might be addressed school-wide.

Source: University of Pennsylvania School of Nursing