Over the last century, widespread use of vaccines has almost completely wiped out contagious diseases such as measles, smallpox and polio. Today, these diseases may come roaring back to life, not because of any medical failure, but because of deliberate neglect to stop it.

Although all children must be immunized under law before entering school, 48 states allow for religious exemptions and 18 states allow personal belief exemptions to immunization. Allowing vaccine exemptions may seem like a reasonable compromise between public health and private freedoms, but in reality it unfairly puts the general population and children at risk without good cause.

In order to keep down preventable diseases and to protect the health of vulnerable individuals, policy makers should tighten vaccine exemptions.

When individual parents opt out of vaccinations for their children, they put their entire community at risk. To be effective, vaccinations must create herd immunity, which is when the vaccination of a significant portion of a population provides a measure of protection for individuals who have not developed immunity.

If a large enough percentage of the population is vaccinated, individuals who are too young, too ill or unwilling to be immunized will still be protected from diseases. When a large enough number of people choose to forgo immunization, though, herd immunity starts to break down, letting disease spread.

Already the consequences of herd immunity breakdown are showing. Take measles, for instance. Measles used to affect 3 million children and kill 500 children a year, but it was declared to be eliminated in 2000 and reduced to an average of barely 200 cases annually thanks to vaccine use.

Last year, when the number of vaccine opt-outs increased nationwide, the number of measles cases skyrocketed to 644. This year, measles continue to make headlines as this contagious disease has already affected 84 people and caused an outbreak of 59 cases in Anaheim, Calif., and is quickly spreading to other states.

Even this high rate shrinks in comparison to the global rate of measles, though. According to Dr. Frieden, the director of the Centers for Disease Control and Prevention, a child dies every four minutes from measles complications worldwide. Creating herd immunity through vaccine use is necessary to prevent such widespread cases in the United States.

Despite the vaccine’s clear progress towards preventing the spread of disease, fear of vaccines overwhelms reason. Generally, disapproval of vaccination comes from either religious opposition or from individuals who link vaccines with negative side effects such as autism.

While convincing someone with religious convictions against medications that vaccines are safe would be difficult, it should not be so difficult to debunk scientific opposition. To prove the link between vaccines and autism, most anti-vaccination proponents cite a paper by British scientist Andy Wakefield that was withdrawn from the medical journal Lancet and was later entirely debunked.

Since then, the strongest proof of a link between vaccination and autism has been statistics showing that one in 50 vaccinated children develop autism. Even this piece of evidence relies on the faulty idea that correlation is causation.

The anti-vaccine movement relies less on concrete evidence that vaccine harms individuals and more on a general distrust of the scientific community and fear of the unknown. Vaccine critic Barbara Loe Fisher says, “Public health officials and pediatricians are not infallible. What is considered scientific ‘truth’ today may not be true tomorrow.”

Fisher might be right that we do not know literally everything about the possible side effects of vaccination. However, the burden of proof lies on Fisher and other vaccine critics.

Based on widespread understanding backed by scientific experts and peer-reviewed scientific journals, vaccines have virtually eliminated key diseases that still continue to harm and disable people in other countries. It makes no sense for people to avoid a procedure with clear benefits for fear of side-effects that have not yet been proven.

Parents should have the freedom to act on their religious and personal beliefs, even if those beliefs may not always make sense or are based on fear. However, this freedom extends only so far until it encroaches on the broader community and the rights of a child.

Parents who choose to opt out of vaccines likely mean well and deserve to be treated with respect. This does not excuse the fact that failing to immunize children puts individuals with weak immunity systems and children at risk without their consent.

NPR recently highlighted the story of Carl Krawitt, a father raising his 6-year-old son Rhett struggling with leukemia. Rhett’s leukemia prevents him from receiving a vaccine until his immune system has developed enough to receive treatment. Until then, Rhett relies on herd immunity to stay safe from harm.

Problematically, Rhett attends Reed Elementary school in Marin County, Calif., a school where the personal vaccine exemption rate hovers at the extremely high rate of 7 percent.

Krawitt, who rightly fears for his son’s safety, put it best when he said, “If you choose not to immunize your own child and your own child dies because they get measles, OK, that’s your responsibility, that’s your choice. But if your child gets sick and gets my child sick and my child dies, then … your action has harmed my child.”

Parents like Krawitt should not have to fear sending their children to school at the risk of catching contagious diseases. While Rhett may be a rare case, no child should be put at risk when safe solutions to the problem are so readily available.

The debate over vaccine opt-outs comes down to fear. If vaccine exemptions continue to rise, it will be based on misinformation and unfounded fears. Instead, the general public should avoid willingly returning to a time in which parents feared that their children might catch measles.

Allowing preventable diseases to come back and threaten the health of many would be a huge mistake. States that allow for loose philosophical exemptions should tighten their opt-out programs by eliminating the personal belief exemption and requiring a doctor to sign off on all religious exemptions. If not, the consequences could harm individuals just like Rhett.