Nearly every state in the Union offers parents an exemption from vaccinating their children based on their religious beliefs — despite research showing that virtually no organized religion declares an opposition to vaccinations.

Religious waivers have been widely exploited by vaccine skeptics throughout the U.S. because applicants aren’t actually required to show evidence of faith-based objections to vaccinating their children. Anti-vaccine groups even go as far as to teach parents how to game the religious exemptions.

Vaccine waivers have come under increased scrutiny in recent weeks, as a major measles outbreak that began in California’s Disneyland park spread to 17 states. California is among 20 states that have laws that go beyond religious exemptions and allow parents to cite a “personal belief” or philosophical objection to vaccines.

There’s little difference between those exemptions in practice. In the case of religious waivers, the process for parents to obtain an exemption boils down to little more than stating in writing that it would violate the parent’s religious tenets to vaccinate his or her child. State officials must trust that the parent is acting on a sincere or truly held belief.

That leaves plenty of room for parents who do not want to vaccinate their children for a number of personal reasons, be it a belief that a certain vaccine is unsafe or a desire to stay away from vaccine “toxins,” to game the system where a personal belief option is not available to them.

John Grabenstein, a retired Army colonel and former director of the Military Vaccine Agency who now works for Merck Vaccines, did an extensive analysis of religion and vaccines for a 2012 study published in the journal Vaccine.

Grabenstein told TPM in a recent phone interview that based on his research, it’s clear that parents who requested religious exemptions to vaccinating their children were pursuing a waiver out of some safety concern, not because their faith prevented them from vaccinating their kids.

“When you boiled it down to what’s your objection, it was a safety concern in a cluster of people who have the same religion,” he said. “It was not a matter of theology.”

Virtually no major religion has stated opposition to vaccination. Grabenstein said that the Quran, the Bible and the Torah are consistent in saying it’s important to preserve life, and by extension vaccinate.

Christian Scientists, who avoid doctors at all costs in favor of healing through prayer, are an exception.

Grabenstein argued that two other anecdotal examples of religious opposition to vaccination, the Amish community and Catholics, don’t hold up to scrutiny.

“There’s nothing in the Amish faith that says don’t get vaccinated,” Grabenstein said, attributing Amish enclaves’ avoidance of vaccines to their reclusive behavior. “When the county health department people go talk to the Amish elders, they very frequently will get the kids vaccinated.”

Catholics do take issue with certain vaccines, including the rubella vaccine in the combination measles-mumps-rubella (MMR) shot, that are made from viruses grown in cell lines that descended from two voluntarily aborted fetuses in the 1960s.

But the Catholic Church does not compel parents to avoid those vaccines.

The Vatican’s Pontifical Academy for Life clarified in 2005 that parents should seek out alternative vaccines to the “tainted” ones made from fetal cell lines. Where there is no alternative vaccine available, the academy stated that the moral obligation to use the “tainted” vaccine outweighs concerns about its origin.

The absence of stated opposition to vaccinations in virtually all religious doctrines doesn’t prevent those skeptical of vaccines from claiming the exemption, though.

The anti-vaccine group National Vaccine Information Center, which pushes the debunked theory that vaccines are linked to autism, advises parents with “sincerely held” personal and spiritual beliefs against vaccination to claim religious exemptions. The group’s president, Barbara Loe Fisher, offered strategies for doing just that in a 2011 conversation with Dr. Joseph Mercola, who runs a controversial alternative medicine website.

“You do not have to belong to a ‘church’ or an organized religion that ‘officially opposes vaccination’ to take a religious exemption to vaccination,” Fisher said, marking air quotes with her hands around certain phrases. “States that have legal language that restrict your ability to take a religious exemption to vaccination based on the fact, for example, you don’t belong to a church — whenever that’s been challenged at the high court level it’s always been found to be unconstitutional.”

Fisher later hinted that sincerely held religious beliefs can include a fear of what may happen to the child after he or she is vaccinated.

“We must defend the religious exemption to vaccination at all costs,” she said in the video. “It’s all that stands between us and a militant, oppressive forcing of vaccination by those who have at this point in time no accountability or liability for what happens after those vaccines are given.”

It’s tough to nail down exactly how many parents request religious waivers in each state due to differences in reporting methods.

Tens of thousands of parents of kindergarten students take advantage of both personal belief and religious exemptions, according to data from the Centers for Disease Control and Prevention. California led the pack in total non-medical exemptions for the 2013-2014 school year with a whopping 17,253 waivers for kindergartners, followed by Michigan and Texas with over 6,000 and 5,000 waivers, respectively. Florida, which grants only religious exemptions, still reported nearly 4,000 waivers for the grade.

Just two states, Mississippi and West Virginia, restrict vaccination exemptions to parents who have a medical reason for not vaccinating their children. Last week, West Virginia legislators stripped language from a bill that would have granted a religious exemption.

States beyond California are now rushing to curtail personal belief exemptions in light of the latest measles outbreak, too. But even if they do, it’s clear that vaccine skeptics will still have a workaround to obtain a waiver.