Compulsory coronavirus vaccination has been a specter hovering over vaccine skeptics throughout the pandemic, but the issue is coming to a head, after President Biden announced federal mandates affecting up to 100 million Americans and such enormous institutions as the Los Angeles Unified School District mandated vaccinations, too.

Opponents of vaccination mandates are ready to fight and are aiming to use religious, philosophical and personal-belief exemptions to abstain from required vaccinations. The history behind the process for gaining such an exemption suggests that those seeking religious exemptions to the coronavirus vaccination mandates will not be widely successful. In recent years, many states, including California, Connecticut, New York, Maine and Vermont, rolled back personal-belief exemptions from mandatory vaccination, making it nearly impossible to claim that individual convictions prevent you from being vaccinated.

Part of the issue lies in what constitutes a religious reason (and who gets to determine its sincerity).

Historically, nonmedical exemptions to mandatory vaccines fall under two categories: religious belief and philosophical conviction. In a legal system that generally defines religion by the Protestant-centric criteria of an individual’s “sincere belief or faith,” the two categories are largely a distinction without a difference. Since most traditional religious institutions do not oppose vaccination, personal beliefs, whether “religious” or not, have been the only way for individuals to avoid vaccination mandates. But as anti-vaccination activism has gained power and we have seen outbreaks of contagious, once-contained illnesses, legislators have steadily dismissed religious or philosophical conviction as a viable reason to abstain from vaccination.

Opposition to compulsory vaccination is as old as vaccination itself, dating to mandated smallpox inoculations in the 19th century. Between the Progressive Era and the 1950s, local governments generally relied on campaigns of “persuasion” rather than coercion to encourage vaccination. When the rate of polio and then measles vaccinations dipped, however, many states adopted mandates for school attendance in the 1960s and 1970s.

Scholars date modern opposition to vaccination to the exposé documentary “DPT: Vaccine Roulette,” which aired numerous times on the NBC Washington-area affiliate station in April 1982 before being excerpted and shown nationally on the “Today” show. The documentary suggested that the pertussis (whooping cough) portion of the combined diphtheria-pertussis-tetanus (DPT) shot, given to infants beginning in 1948 and required for school attendance, could cause brain damage.

“Vaccine Roulette” catalyzed a grass-roots movement of parent-activists. This group, now the National Vaccine Information Center, advocated for greater transparency about vaccine safety and ingredients, financial compensation for victims of vaccine injury and an alternative version of the vaccine.

Congress passed the National Childhood Vaccine Injury Act in 1986 (under which the National Vaccine Injury Compensation Program was created), and, after enough parents abstained from giving their children DPT shots and vaccine manufacturers saw significant financial losses, the vaccine was reformulated into an acellular version in the early 1990s (now the DTaP) known to have fewer possible side effects. Armed with 50 years of scientific data and the backing of sympathetic lawmakers, the parent-activists’ objectives were largely accomplished.

Rather than being quelled by DPT’s reformulation, however, vaccine hesitancy actually grew stronger. Throughout the 1990s and early 2000s, alternative health practices boomed in popularity, and more Americans started to emphasize “natural” approaches to health and medicine.

Often these devotees were White, middle-class women. The natural-parenting movement also emphasized a “back to nature” approach that contributed to skepticism of childhood vaccinations. These movements shared a distrust of big, authoritative institutions, be they pharmaceutical companies, the American Medical Association, churches or the federal government. Instead of looking to previously trusted authorities, individuals shopping in the marketplace of goods and ideas trusted their intuition and “alternatives.”

Mercury, the heavy metal, became a source of concern because of its presence in foods, medications and vaccines, including thimerosal, an ingredient in the measles-mumps-rubella (MMR) shot. In 1997, the American Academy of Pediatrics and the Public Health Service recommended removing thimerosal from the MMR shot even though it posed little threat to the safety of children. It was an attempt to alleviate unfounded anxieties about toxicity surrounding the much-debunked theory that mercury was a cause of autism.

Yet, this move only strengthened the resolve of the anti-vaccination movement, which now included some advocacy groups of parents with children diagnosed with autism during the 1990s, including those popularized by Jenny McCarthy, some alternative-medicine proponents and some libertarian conservatives who lobbied for “medical freedom” and “health choice.”

Fear of bodily pollution by the preservatives in vaccines amplified during the 1990s-2000s, as the number of vaccines brought to market and added to children’s mandatory immunization schedules rapidly increased. And more people were paying attention to the ingredients in vaccines themselves. For a small but vocal slice of Americans, vaccines became a controversial topic rather than a routine medical procedure.

In contrast with how the specific complaints about DPT safety were spurred by demonstrable scientific evidence and taken seriously in Congress, later vaccine skeptics’ focus on everyday chemicals and their hostility toward “Big Pharma” and the government’s role in mainstream medicine left them marginalized rather than validated by officials. The Internet provided a gathering place that allowed these activists to foment concern and share misinformation.

Their emphasis on the concept of bodily pollution and autonomy resonated with many religious and spiritual traditions, but given the absence of scientific data to justify claims of poor safety, these concerns were generally considered unscientific and laden with conspiracy or politics by the scientific and media communities.

From 2003 to 2007, the number of parents seeking and receiving religious exemptions from vaccination for kindergartners doubled or tripled in 20 of the 28 states where religious and philosophical exemptions were allowed at the time.

Public health officials and lawmakers started to deem exemptions too risky and to suspect that they were being abused. In other words, too many parents were using the defense of religion or personal belief to keep their children unvaccinated, jeopardizing herd immunity. In most cases, religious leaders and institutions espoused pro-vaccine stances on a communitarian moral logic: Unvaccinated people endangered the health of others, which is immoral. Yet, abstainers could still make personal-belief statements to avoid vaccinations without the approval of a religious authority.

Rather than pressing for changes to the formulations of vaccinations, as their predecessors had for DPT, this movement’s goal was to opt out of vaccination (or specific vaccines) altogether, and to use state exemption policies to do so without being excluded from schools.

The result? Outbreaks of measles, the all-but-eradicated, highly contagious childhood illness, flared across the country in the mid-2010s. In the hot spots with outbreaks, religious and philosophical exemptions were proportionally higher and more children were unvaccinated than in the rest of the country.

Outbreaks often spread outward from pockets of insular communities, including evangelical churches with vaccine-skeptical pastors, Ultra-Orthodox Jews in New York, the Amish in Ohio or the progressive private Waldorf schools, to unvaccinated children in nearby areas whose parents had attested to a religious opposition to vaccination.

During the measles outbreaks, some states required a signed affidavit from a religious leader to validate a religious exemption request, while others, mostly with Republican-led legislatures, attempted to make it easier to claim religious reasoning.

In 2015, an outbreak of measles traced to Disneyland led California to ban religious and philosophical exemptions entirely. More states, such as New York, Connecticut and Maine, banned these exemptions just before or during the coronavirus pandemic.

Today, 42 states allow some form of religious exemption and 14 states permit personal conviction as reasons to abstain from mandatory vaccinations in public schools. But with all major religions supporting vaccination, coronavirus vaccine opponents’ desires to avoid immunization will have little institutional backing or traditional religious doctrine to support their attestation to beliefs opposing vaccination. That probably means they aren’t likely to gain religious exemptions. For adults in workplace settings, support from organized religion for vaccines could make declarations of sincere religious belief seem dubious, particularly given the widespread politicization of coronavirus vaccination.

Since religious exemptions are determined by individual states, there is no simple rule about how these laws will be applied in the future. But what the recent history shows is that, when faced with a public health crisis or outbreak, many states will be loath to accept religious or personal-conviction exemptions from mandatory vaccination, particularly when faith leaders, public officials or doctors must determine the root of abstainers’ sincerity.