Parents are delaying vaccinating their children out to fear of “overloading” their immune system. This delay, however, has resulted in an outbreak of vaccine preventable diseases.

Parents across the nation are delaying, or even preventing, the vaccinations of their children out of fear of harming their child, or for religious purposes. However, this delay has led to an increase in the number of cases of virtually extinct diseases, such as the measles, mumps, and pertussis. All of these diseases can be avoided through vaccinations. The longer a parent waits to vaccinate their child, the more at risk their kids are to contract these and other diseases.

The fears of vaccines have stemmed from two major causes: a flawed article that linked vaccinations to autism, and an increase in the number of vaccines available to children today. The article, released 20 years ago by medical journal The Lancet was written by Andrew Wakefield and linked the measles, mumps, and rubella vaccines to causing autism in children. While the article was eventually removed from the journal and Wakefield de-licensed from medicine, the damage had already been done.

It took nearly two decades for immunization rates to return back to normal, but recently, those rates have begun to drop again.

According to The Washington Post, parents feel that if they delay their child’s vaccination schedule they are less likely to “overload” their child’s immune system and cause harm.

The Center for Disease Control (CDC) states that vaccines are they safest they’ve been in years and don’t overwhelm the immune system. Over the last 20 years, scientists have decreased the number of antigens by nearly 96% to make it safer for children to receive more than one shot at once.

Antigens are like tags on the surface of a viral protein that the body uses to identify the molecule as foreign. When the body notices these foreign substances, it creates a group of defense proteins called antibodies. Vaccines carry just enough of a virus’ antigens to allow the body to make the specific antibodies to fight the disease in the future without infecting the child.

The number of vaccines available to children has increased from eight to 14 over the last 30 years , but the viral content of each vaccine has decreased, according to The Washington Post.

Each vaccine has a viral body count of about 150, whereas in the past, the viral count has been about 3,000. This change was made to ensure that vaccines are the safest they can be. The CDC says that vaccines are designed to give a baby a fraction of the antigens they encounter during an average day.

The only thing delaying vaccines in children does is increase their chance of contracting vaccine preventable diseases, says the CDC. The American Psychological Association (APA) has found a correlation between the increase of vaccine preventable diseases and the number of parents delaying their child’s vaccination schedule.

Take measles, for example. In 2000, the measles virus was basically unheard of because of the vaccinations that helped children fight against it. However, since the vaccination-delay movement, the infection rate for measles has nearly doubled. Since 2001, about 2,012 measles cases were reported in the U.S. Nearly 70% of those patients were unvaccinated, according to TIME. While the patients ranged all ages, the majority of them were babies 6-15 months old.

While the parental fear is very real, the outcome of their actions have had very negative effects. The only true way to prevent the outbreak of diseases like measles and mumps again is to stop delaying the vaccination schedules.