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Vaccines protect children and communities from diseases that once spread quickly and killed thousands of people.

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Over the past 60 years, childhood diseases such as measles, mumps, and whooping cough have declined dramatically because of widespread immunization of infants. A vaccine is a small dose of inactive virus that is injected into the body to stimulate the production of antibodies to guard against the disease. Vaccines control infectious diseases that once spread quickly and killed thousands of people.

Vaccines are administered early in life because many preventable diseases are more common in infants and young children. Vaccinations protect the child, as well as those in the child’s community. An immunized person is less susceptible to a disease and less likely to transmit it to others. State laws require schoolchildren to be fully immunized, a requirement that has increased vaccination rates and prevented many diseases.

The Centers for Disease Control and Prevention (CDC) recommends that infants be vaccinated against most vaccine-preventable diseases by the time they are 2 years of age. Vaccination rates have increased markedly over the past 15 years. The proportion of children aged 19 to 35 months receiving the recommended series of vaccines increased from 69% to 83% between 1994 and 2004. However, the rate has stalled since, standing at 82% in 2013 (Child Trends Databank, 2015).

Why are nearly one fifth of children unvaccinated? One reason is that many families in the United States do not have access to the health care they need. Children in families with incomes below the poverty level are less likely to receive the combined series vaccination (Child Trends Databank, 2015). Many parents are unaware that children from low-income families who do not have medical insurance can receive vaccinations through the federal Vaccines for Children Program, begun in 1994. In addition, the vaccination schedule is complicated, with specific vaccines administered at specific times in development (Kurosky, Davis, & Krishnarajah, 2017).

Another, more troubling, reason for the stalled vaccination rate is the common misconception that vaccines are linked with autism. Some parents refuse to have their infants vaccinated due to this concern (Salmon, Dudley, Glanz, & Omer, 2015). Extensive research indicates that there is no association between vaccination and autism (Modabbernia, Velthorst, & Reichenberg, 2017; Taylor, Swerdfeger, & Eslick, 2014). Instead, children tend to receive vaccines at the age when some chronic illnesses and developmental disorders—such as autism—tend to emerge, but this correlation is not indicative of a cause-and-effect relationship. (Recall from Chapter 1 that correlational research documents phenomena that occur together but cannot demonstrate causation.) While specific causes of autism spectrum disorders have yet to be fully identified, we do know that autism has a strong genetic component and is also associated with both maternal and paternal age (B. K. Lee & McGrath, 2015; Waltes et al., 2014). Other parents report concerns about chemicals in vaccines and possible unforeseen future effects (Martin & Petrie, 2017). Longitudinal research has suggested no negative long-term effects of vaccines administered in infancy (Henry et al., 2018; Su et al., 2017; Wessel, 2017).

Even when children receive the full schedule of vaccinations, many do not receive them on the timetable recommended by the National Vaccine Advisory Committee. Vaccine timeliness is important because the efficacy of early and late vaccination is not always known and may vary by disease. When a child receives a vaccination may be just as important as whether the child receives it in promoting disease resistance.