As measles cases hit a 25-year high in the United States, Texas medical experts fear the state could see the next outbreak of a vaccine-preventable disease. Texas has reported 15 confirmed cases of measles so far in 2019, six more than in all of 2018.

Health officials are watching pockets of Texas closely because of the number of parents requesting exemptions under Texas’s broad vaccine exemption law. Texas is one of 16 states that allow parents to bypass vaccine requirements for enrolling their kids in school by claiming a conscientious exemption, along with citing medical or religious concerns. Just last month, Washington ended conscientious exemptions on the heels of a large measles outbreak with over 70 reported cases. Three states — California, West Virginia and Mississippi — only allow medical exemptions.

Texas’ exemption law used to be stricter. In 2003, a state senator proposed loosening restrictions via a three-page amendment to a 311-page bill. After five minutes of discussion, the amendment was approved. The bill was soon signed into law. Sixteen years later, former state Sen. Craig Estes said the change to Texas' vaccine laws that he helped enact should be reviewed in the current public health climate.

“Obviously we didn’t ever imagine what would happen,” Estes, a Republican from Prosper, told The Texas Tribune. “With what’s happened recently, I would encourage the legislature in the future to revisit that issue and debate it.”

The speedy way in which the Texas Legislature weakened the state's vaccine exemption rules suggests that, like Estes, few in office at the time thought it would put Texas at risk for future outbreaks. However, while experts suggest Texas is now vulnerable, efforts to change the exemption law have been dead on arrival in the Capitol.

“There will be a terrible measles epidemic in Texas, and children will be hospitalized in intensive care units, just like they are in New York right now,” Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, said last month. “That will wake up the state Legislature to realize that there's a problem and close those exemptions.”

Tracking Texas exemptions

Kindergarteners must have 10 immunizations to be enrolled in Texas schools. Since 2006, when the state first started reporting the data, the exemption rate for kindergarteners in Texas has risen from 0.3% for the 2005-06 school year to 2.15% for the 2018-19 school year.

In Texas, school districts, private schools and charter schools are required to report their vaccine exemption rates per vaccine. The data collection is done through a survey administered by the Texas Department of State Health Services, but some schools don’t report consistently, leaving gaps in the data.

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The data shows certain communities — like the Dallas Independent School District — have seen a recent spike in conscientious exemptions for kindergarteners. Others — like El Paso ISD — have seen exemptions recently plummet. Some smaller private schools, meanwhile, have exemption rates that are significantly higher than those of other schools. The Austin Waldorf School had the highest vaccine exemption rate for the 2018-19 school year, at 52.9%. Alliance Christian Academy had the second-highest rate at 40.6%.

When enough of a community is immunized against a disease, that group has what's known as herd immunity, meaning there is a low risk of a disease spreading. Vaccine-preventable disease have different herd immunity thresholds. Measles, which is highly contagious, has a high herd immunity threshold of 95%. According to a state report for the 2018-19 school year, Texas kindergarteners statewide had coverage levels higher than 95% for all required vaccines. Yet the data from individual school districts and private schools suggests that some communities may fall short of meeting that threshold for some vaccines.

A five-minute discussion

Before 2003, the state’s education code gave parents two options to exempt their children from vaccines: submit a medical exemption form signed by a physician or sign an affidavit affirming that administering a certain vaccine conflicts with “the tenets and practice of a recognized church or religious denomination."

State lawmakers voted that year to dramatically expand who could secure nonmedical exemptions when they approved House Bill 2292, a 311-page bill that overhauled the state’s sprawling network of health and human services organizations by consolidating 12 state agencies into five, saving the state $1 billion. The bill was a high priority as lawmakers were scrambling to address a $10 billion shortfall, recalled former state Rep. Talmadge Heflin, one of the bill’s co-authors.

Estes’ vaccine amendment struck out the language limiting religious exemptions to vaccines violating the tenets of “a recognized church or religious denomination.” He replaced that with the more vague “religious belief” and added a new exemption category: “reasons of conscience.” The amendment also lowered the bar for medical exemptions, allowing a doctor to sign off if he or she thought the vaccine would "pose a significant risk" instead of the previous requirement that the vaccine "would be injurious" to a child.

When Estes introduced the amendment on the Senate floor in 2003, he spoke about providing an option for parents who wanted to opt out of a vaccine for nonmedical reasons, such as if a sibling had an “adverse reaction” to it. He did not mention the broadening of the religious language or explain the reasoning behind adding “reasons of conscience” to the state statute. He praised a provision requiring the state to give parents pursuing a conscientious exemption for a child additional paperwork warning them about the potential health risks of not immunizing their kids.

“What I like about this amendment the most is the fact that we make sure that the affidavit that they fill out by the Department of Health explains to them the consequences of not immunizing their children, and thereby I hope that it increases the awareness of how important it is to have immunizations,” Estes told his fellow senators.

Estes' amendment did not come out of blue. Dawn Richardson, advocacy director for the National Vaccine Information Center, was among those lobbying for Texas to adopt a conscientious exemption system in 2003. She said the conversation around that issue started in the 1997 session, but there wasn't significant movement until a 2001 bill loosening the exemption system passed out of a House committee but failed to make it to the floor for a vote before the full House. Still, the issue had not been thoroughly debated among the full House and Senate.

"It was a seven-year process over which many bills were filed," Richardson said. "Like many pieces of legislation that are working to shift these sort of things, sometimes it takes several sessions to work with different legislators to move things forward."

The success of Estes' amendment on the Senate floor was shaped in part by the discussion around vaccines at the time.

Measles had been declared eliminated from the United States just three years earlier in 2000. Seth Mnookin, director of the graduate science writing program at the Massachusetts Institute of Technology and author of “The Panic Virus: The True Story Behind the Vaccine-Autism Controversy,” said the declaration was a medical milestone that may have inadvertently led to reducing fears about others catching the disease in the future.

“Even for vaccine advocates, who were very concerned about the possibility of measles outbreaks and knew how dangerous measles was, even with that, there was this sense that concern was almost notional,” Mnookin said. “In some ways, what we saw there — and we see this again and again with vaccines — is vaccines were victims of their own success.”

Former state Sen. Leticia Van de Putte said she worked with Estes to narrow the wording of the amendment, which she called “pretty vague” when she first read it.

Van de Putte, a San Antonio Democrat, recalled vaccines were drawing concerns at the time, in part related to thimerosal. The preservative, which contains small traces of mercury, was commonly used in multidose vaccines to prevent contamination between doses. In 1999, a review by the Food and Drug Administration found there was no evidence that the mercury caused harm but that in certain cases, the amount could be higher than the recommended mercury exposure by the World Health Organization. In 2001, vaccine makers removed thimerosal from all of the U.S. vaccines recommended for children under 6, except for the flu vaccine.

The conflicting warnings about thimerosal raised concerns that vaccines were unsafe.

“That’s what we really looked at at the time,” Van de Putte said. “Now if you look at the data since then, we know that not to be the case."

Along with the thimerosal controversy, a now-discredited study linking the MMR (measles, mumps and rubella) vaccine to autism also prompted concerns at the time, said Rekha Lakshmanan, advocacy director for The Immunization Partnership, a vaccine advocacy nonprofit. Lakshmanan pointed to the 1998 study from Andrew Wakefield, a British gastroenterologist who lost his medical license in 2010 and now lives in Austin, as a pivotal source of the anti-vaccine movement today.

Once Texas' less restrictive vaccine exemption system went into effect on Sept. 1, 2003, public health experts expressed concern about how many parents would take advantage of the new conscientious exemption option.

"We don't know how many to expect," Doug McBride, a spokesperson for the state health department, told the Fort Worth Star-Telegram in 2003. "From the public health protection perspective, we hope it's not very many, but it is a legal option. We ask parents to base their requests for exemptions on accurate information."

State data suggests that in the 16 years since Texas loosened its exemptions system, the number of families taking advantage of it has grown dramatically. The state tracks how many requests for affidavits it receives each year — though some of the forms are never submitted. In the 2004 fiscal year, Texas received vaccine exemption affidavit requests on behalf of 7,250 individuals. By 2018, that number had grown more than tenfold to 76,665 individuals.

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A new anti-vaccine movement

After 2003, the next significant turning point for the anti-vaccine movement in Texas came 12 years later.

“There’s always been a very small minority group who has been vocal and opposed to vaccines,” Lakshmanan said. “But in 2015, things changed, and there was a new iteration of vaccine deniers and anti-vaccine advocates.”

That year, as outbreaks of measles and whooping cough began to rise in pockets of Texas and other parts of the country, state Rep. Jason Villalba filed a bill hoping to remove the conscientious exemption option from state law. House Bill 2006 aimed to limit exemptions for vaccines to a “specified and verifiable religious-based reason,” according to the bill's text. Villalba said it was an attempt to keep children safe from vaccine-preventable diseases.

“We are just saying, 'Look, if you are going to send your children to public schools, they need to be vaccinated,'" Villalba, a Dallas Republican, said in 2015.

The response to Villalba's bill marked a shift in the language of vaccine critics from "anti-vaccine" to emphasizing "vaccine choice" and "medical freedom."

Jackie Schlegel, who lives outside Austin, said when she heard about Villalba’s bill, she and other mothers organized a rally at the Capitol to oppose it. Texans for Vaccine Choice, was born and the group has remained active at the Capitol ever since.

“Texas has a long history of really valuing parental rights, and that's what this has been about for us,” Schlegel, the group's president, said in May to dozens of supporters at the Texas Capitol. Standing beside her was Robert F. Kennedy Jr., one of the country’s most prominent vaccine critics, who traveled to Austin for the event.

Since the 2015 session, Texans for Vaccine Choice has advocated against changes to the state’s exemption law and against efforts to increase access to vaccine exemption data.

When state Sen. Kel Seliger, R-Amarillo, laid out a bill this year that would have allowed the public to access vaccine exemption rates by individual schools rather than just by school districts, several members of Texans for Vaccine Choice testified against it. They said it would lead to increased bullying and single out children who have exemptions. Seliger’s bill, like every other vaccine bill filed this year, went nowhere.

Hotez, one of the most prominent vaccine advocates in the country, found himself a target of defenders of the current system in Texas as he urged lawmakers to consider some vaccine-related bills this session. In a heated exchange on Twitter between Hotez and state Rep. Jonathan Stickland, the Bedford Republican called vaccines “sorcery to consumers.” However, in an interview with The Dallas Morning News, Stickland clarified that he vaccinates his children but supports parents' right to choose whether and when to vaccinate their children.

Hotez warned it may take a measles epidemic hitting the state to lead to changes in the exemption law, in the same way the Disneyland measles outbreak in 2015 led to California passing legislation tightening its vaccine exemption system to allow only for medical exemptions.

Texas has reported 15 confirmed cases of measles this year through May, the highest number of measles cases the state has seen since 2013. However, there has not been a single confirmed outbreak — defined as three or more related cases — this year so far. Despite the lack of state outbreaks, Hotez said, the state's current system for vaccine exemptions will continue to pose a public health risk.

"Texas has so far dodged a bullet in terms of a really terrible measles epidemic, like in New York," Hotez said. "But it's only a matter of time."

Disclosure: Baylor University has been a financial supporter of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune's journalism. Find a complete list of them here.