Over the last 200 years, vaccines have proven to be one of the most effective ways to prevent and control disease. Many centuries-old diseases have been eradicated or pushed to the brink of extinction thanks to vaccination – the last smallpox case in the world occurred in 1977, and the global incidence of paralytic polio has dropped 99 percent since 1988. In the United States alone, vaccines have prevented more than 732,000 deaths and 21 million hospitalizations over the last 20 years.

Thanks to the drastically reduced burden of vaccine-preventable diseases in the United States, many young parents have never seen a case of vaccine-preventable disease like measles encephalitis. This may be causing some parents to believe that a perceived risk of vaccinating infants outweighs the benefits of protecting them from infection with these diseases. Much of this concern arises from a now-debunked study incorrectly claiming a link between childhood vaccination and the development of autism, though some parents say they are concerned about the number of immunizations the CDC recommends children receive before their second birthday.

Fortunately, parents opting to forgo immunization altogether are the minority – the CDC estimates 99.4 percent of children have received at least one vaccination; that means that less than one percent of children in the United States is completely unvaccinated. However, some parents are deciding to delay the CDC-recommended immunization schedule rather than decline vaccination altogether, despite the fact that there is no evidence to suggest that a healthy child’s immune system will be affected by receiving several vaccines at one time. Recent data indicates that less than 75 percent of children between 19 and 35 months old in the U.S. have received the combined seven-vaccine series that protects against serious diseases like polio, diphtheria and pneumococcal pneumonia. The CDC recommends against altering the vaccination schedule so strongly that it has even created a “catch-up” schedule for children whose vaccinations have been delayed so they can get back on track as quickly and safely as possible.

Such delay or refusal of childhood immunizations is dangerous both for the child and for public health. Though prolonging the vaccination schedule recommended by the CDC has not been shown to be safer for the child, it does put the child at increased risk of serious complications or even death due to infections they would otherwise have been protected against. A key reason why children are vaccinated before they are two years old is that many of these diseases pose a significant threat to young children; the protection conferred by these vaccines simply can’t wait.

Altering the recommended childhood vaccination schedule also threatens public health by interfering with “community immunity,” a form of indirect protection that certain vaccines confer on a population when vaccination rates are high. Community immunity can be most simply described as a reduced risk of exposure to a disease thanks to low levels of the disease in a highly vaccinated population. For example, pneumococcal vaccination induces strong protection from disease, reducing the incidence of pneumococcal pneumonia, meningitis and ear infections even in unvaccinated members of a community. This indirect protection is important for public health and safety because it protects vulnerable groups from disease, like those with compromised immune systems or those who can’t be vaccinated because they are too young.

Community immunity is weakened or disappears when vaccination rates aren’t high enough, leaving vulnerable groups like infants and the infirm at greater risk of disease. As a result, the recent decline in vaccination rates in some areas of the United States over the last few years has raised concerns within the public health community. Parents delaying or refusing to vaccinate their children – and the resulting loss of community immunity – has led to a resurgence of vaccine-preventable diseases previously thought to no longer threaten public health. Though measles was declared eliminated in the U.S. over a decade ago, a recent outbreak attributable to vaccine refusal in southern California resulted in 125 measles cases, including 12 infants who were too young to be vaccinated against the disease.

With the decision to immunize children comes the important responsibility to protect the lives of both the child being immunized and of other vulnerable community members. Pediatricians, scientists and public health experts agree: vaccines are safe, vaccines are necessary and vaccines work. The data on the safety, impact and results of immunizations are robust and irrefutable. They have tremendous potential to prevent disease and save lives, but only if vaccine acceptance remains high. Ensuring every child receives the full course of recommended immunizations is essential to wipe vaccine-preventable diseases off the map.