After 18-year-old Ethan Lindenberger gained national attention for updating his immunizations despite his mother’s anti-vaccination beliefs, he and two professors of pediatrics and epidemiology spoke in a hearing to the U.S. Senate Committee on Health, Education, Labor and Pensions on March 5.

Titled “Vaccines Save Lives: What is Driving Preventable Disease Outbreaks?,” the hearing presented research behind 26 vaccinations approved by the Centers for Disease Control and Prevention (CDC). Lindenberger also requested communities like HELP to make their reports more accessible while encouraging the public to rely on healthcare professionals.

“Countless studies have been done to show that vaccines are safe,” Lindenberger said to the Senate. “Charlatans and internet fraudsters who claim that vaccines aren’t safe are preying on the unfounded fears and daily struggles of parents, and they are creating a public health hazard that is entirely preventable.”

Arguments against vaccinations are varied; according to the U.S. National Library of Medicine, parents with religious objections are concerned with the aborted fetal tissue and animal-derived gelatins in the measles, mumps and rubella vaccine. In addition, 30 percent of surveyed parents expressed concerns regarding adverse side-effects

“One of the anti-vaccine moms… unfortunately had first hand experience too,” Linnie Cheatham, a stay-at-home mom, said in her blog on Voice for Vaccines. “Her second baby had had an adverse reaction to a certain vaccine, confirmed by a doctor. Afterwards she decided to not vaccinate any of her kids anymore.”

Most states uphold laws that require some sort of vaccination for children, unless parents request to homeschool them.

According to Shots for School, any student attending a California K-12 school must have vaccinations for: diphtheria, tetanus, pertussis, polio, Hepatitis B, measles, mumps, rubella and varicella. After California SB227 was signed in June 2015, California is the only state to remove personal belief and conscientious, philosophical or religious exemptions from immunization requirements.

“We’ve pretty much eradicated chickenpox if you get the vaccination. The vaccination actually works 100% of the time if the person gets two vaccinations for varicella,” school and registered nurse James Matejcek said. “Now the new law has just come into effect starting in July, so any kid going on to seventh grade not only has to have the TDAP but also have the second varicella vaccination.”

Even with such requirements, California has seen outbreaks like the 2014 measles outbreak in Disneyland. Recently, there was an outbreak in a private Los Angeles school on Feb. 27, leaving 30 students ill, according to the LA Times.

“There’s just a new outbreak that happened in Harbor View Westlake high school and middle school in Los Angeles because of the whooping cough,” Matejcek said. “This shows why the TDAP is so important and why we recommend and why we will not let kids get their schedule when they’re going into seventh grade unless they get that TDAP.”