Families across the United States are sending their young children back to school. School preparations are not limited to buying school supplies. Parents should make sure their children are up-to-date with vaccinations.

Immunization requirements vary from state to state, but vaccination’s benefits to public health are evident across the country. Vaccines are often heralded as one of the greatest health interventions in modern history, credited with saving 732,000 lives and preventing 21 million hospitalizations among children born in the United States since the mid-1990s. Globally, their impact extends even further, with a recent study estimating that childhood vaccination saves up to 3 million lives every year.

In many ways, schools are an ideal environment for the spread of infectious disease. Classrooms and playgrounds, full of shared materials and spaces, provide ample opportunity for bacteria and viruses from an infected individual to travel among other students and teachers. These pathogens can be particularly harmful for individuals like young children who have not been exposed to them before. To avert serious illness, the U.S. Centers for Diseases Control and Prevention recommends that young children get vaccinated against eight infectious diseases before their first day of school: polio, varicella (chicken pox), diphtheria, tetanus, pertussis (whooping cough), measles, mumps and rubella. Parents can safely protect their children against all of these diseases by getting the latest recommended dose of just four vaccines in an annual check-up. The CDC recommends that children receive the final dose of the following vaccines between the ages of four and six.

Inactivated Polio Vaccine (IPV). Most parents today are not worried about polio, but the crippling and potentially fatal disease was one of the biggest health threats to children in the United States as recently as the 1970s. Before the vaccine discoveries of Albert Sabin and Jonas Salk, polio was responsible for more than 15,000 cases of paralysis in the United States annually. Thanks to widespread vaccination efforts, however, no polio cases have originated domestically since 1979, and there were only 37 known cases worldwide in 2016. But in today’s globalized society, disease anywhere can be a threat everywhere. The best way to protect children in the United States against the devastating effects of polio is to ensure they receive all four doses of the IPV, the fourth of which should be administered between their fourth and sixth birthdays, right around the age when children begin attending school.

Varicella vaccine. Varicella, commonly known as chickenpox, is a highly contagious childhood disease known for its ubiquitous blister-like rash. Though most cases of chickenpox are limited to fever and itchy blisters, the varicella virus can be particularly dangerous for pregnant women, the elderly and individuals with weakened immune systems. The two doses of the varicella vaccine, first licensed for use in the United States in 1995, are credited with averting more than 3.5 million cases of chickenpox, 9,000 hospitalizations and 100 deaths annually in the United States. The CDC recommends children receive the first dose between 12 and 15 months of age, and the second dose between children’s fourth and sixth birthdays.

Diphtheria, tetanus, acellular pertussis (DTaP) vaccine. Protection against diphtheria, tetanus and pertussis are all conferred through the DTaP vaccine. Though these disease names are less familiar to most parents than polio or chickenpox, they can led to debilitating symptoms such as lock jaw, pneumonia, seizures, paralysis and brain damage. In the most serious cases, all three diseases can be fatal. Widespread DTaP vaccination efforts led to the elimination of diphtheria in the United States in 2012 and have significantly reduced the morbidity rates of tetanus and pertussis, but, like many other infectious diseases, they can quickly spread if vaccine coverage rates decline just a few percentage points. Children should receive the fifth and final dose of the DTaP vaccine between four and six years of age. For adolescents over the age of 11 and adults, protection is conferred through a booster shot known as Tdap.

Measles, mumps, rubella (MMR) vaccine. Protection against several diseases is similarly provided by two doses of the MMR vaccine, the second of which is recommended between ages four and six. Measles, mumps and rubella are highly contagious, airborne diseases that can cause symptoms ranging from rashes and fevers to respiratory infections and brain damage. Tragically, even though the MMR vaccine is highly effective at preventing the viral diseases, there have been several outbreaks of measles and mumps in recent years due to low MMR vaccination rates. When there is broad uptake of the MMR vaccine, however, these dangerous outbreaks can be prevented. Thanks in part to vaccination, there has been more than a 99 percent decline in morbidity of all three diseases in the United States within the past century.

At a time when infectious diseases are no longer the major killers in communities across the country, it can be easy for parents to overlook the importance of early childhood immunization. But the reality is that diseases like polio, diphtheria, rubella and many others are unfamiliar threats to Americans because of broad vaccine uptake. If parents refuse their children’s recommended immunization schedules, not only are they putting their own children at risk of illness and medical interventions in the future, but also they are endangering the lives of individuals who might not be able to get vaccinated. Incorporating routine immunizations into children’s first-day-of-school preparations is one of the best ways to promote public health and help young children stay healthy enough to enjoy the benefits of education.