(NEW YORK) — Exemptions for immunizations required in school are on the rise in the U.S., leading to concerns among medical experts that diseases like measles could soon make a comeback in many states.

In November, the Centers for Disease Control and Prevention reported that exemptions for immunizations required in school is the highest ever recorded in U.S. history – increasing to an average 3.0% in the 2022-2023 school year, with 10 states now reporting exemptions exceeding 5%. This leaves both vaccinated and unvaccinated children vulnerable to disease outbreaks including measles, experts say.

“There’s 9 million people in this country who can’t be vaccinated. They depend on those around them to protect them,” Dr. Paul Offit, a virologist and vaccine advocate, told ABC News.

In his upcoming book, “Tell Me When It’s Over: An Insider’s Guide to Deciphering Covid Myths and Navigating Our Post-Pandemic World,” Offit gives a historical account of the anti-vaccination movement in the U.S. and explains the rise of non-medical immunization exemptions over time and how these trends relate to the nationwide pushback against COVID-19 vaccine mandates.

ABC News spoke with Offit and other doctors who work in infectious diseases and immunization research to explore what’s driving these trends and understand what the future may hold if immunization exemptions keep rising.

“We mandated vaccines – for the first time in my lifetime at all levels,” Offit said. “And that really upset people … people really pushed back, they were angry.”

Since the start of the COVID-19 pandemic, lawmakers have introduced hundreds of pieces of legislation aimed at rolling back vaccine mandates, largely COVID-19 mandates, but some changes have also impacted childhood immunization requirements.

These legislative efforts largely prevented many statewide COVID-19 vaccine mandates, according to the National Academy for State Health Policy. Since the pandemic began, no state has passed legislation to newly allow a philosophical or religious exemption in the few states that only allow medical exemptions, according to the National Conference of State Legislatures. But in some states, new laws or court rulings have made getting routine vaccines harder.

In July 2021, pushback against COVID-19 vaccines started to spill over to routine childhood immunizations in Tennessee. Efforts to vaccinate more of the state’s population against COVID-19, including teenagers, led to the firing of the state’s medical director, Dr. Michelle Fiscus, and temporarily halted all immunizations to kids and teens in the state. As of May 2023, Tennessee law now requires written informed consent by a parent or legal guardian for any person under the age of 18 to receive any vaccine.

Critics worry this added step of written consent creates an unnecessary barrier that may prevent many kids from getting the shots they need, including some of the most vulnerable kids such as cancer patients who often need extra doses of routine vaccines to mount a full immune response.

Dr. Diego R. Hijano, an infectious disease specialist at St. Jude Children’s Research Hospital in Memphis, Tennessee, told ABC News that this new law doesn’t make vaccines safer, it just makes it harder for parents to agree to vaccines and harder for providers to administer them on time.

“We still do all the things we need to do before the law is implemented. It’s just that this step has delayed us being able to offer all these vaccines under the new law because we’ve had to create these consents and have all this [new process] in place,” Hijano said.

Mississippi is not known for being a national leader in public health outcomes – holding higher rates of obesity, diabetes, heart disease, and infant and maternal mortality than national averages – however, the state’s childhood vaccine rates are an exception.

The CDC reports that Mississippi still holds the highest proportion of vaccinated kindergarteners in the country, but health officials worry these high rates may soon be threatened by the recent court order that went into effect in July 2023 requiring the health department to allow religious exemptions, the Associated Press reported.

“The federal [Covid-19 vaccine] mandates were not we received in many places like ours, and some of that bled over into any type of [vaccine] mandate,” Dr. Daniel Edney, state health officer for the Mississippi Department of Health told ABC news. “This is a situation where it’s extremely frustrating, as the chief public health official and physician, to have 40 years of public health policy and science overruled by two attorneys who don’t [have public health expertise].”

Edney says that Mississippi typically has about 500 medical exemptions a year, but now, they have had over 2,100 non-medical exemptions since July and expect to pass 3,000 total exemptions before the year is over. Currently and concerningly, Edney says non-medical exemptions have been concentrated in a handful of counties in the state that include Hinds County, Ridgeland County, Lamar County, and in some pockets on the Gulf Coast.

Vaccine-preventable outbreaks like measles, polio, and whooping cough are far more likely in areas that have concentrated clusters of unvaccinated people, and since no vaccine is 100% effective, people who are vaccinated can also get sick.

Edney said Mississippi has been fortunate not to need the same level of staffing and resources dedicated to respond to vaccine-preventable disease outbreaks like other states more prone to these outbreaks have, but health officials say that has to change now.

“We have to invest in these investigation [resources] for the outbreaks that will come at some point down the road,” Edney said.

Measles cases drove California to tighten vaccine restrictions

Doctors worry that the only thing that will drive this rising trend of non-medical vaccine exemptions in the opposite direction will be disease outbreaks that predominantly affect young children, which was seen in California after there was a large measles outbreak that began at Disneyland from December 2014 to February 2015.

Dr. Dean Blumberg, professor and chief of pediatric infectious diseases at UC Davis Children’s Hospital explained to ABC News that California previously allowed both philosophical and religious vaccine exemptions, but now has some of the strictest vaccine laws in the country through state legislation passed in 2016 and 2019, which only allows medical exemptions that the health department reviews.

“I think vaccines are always at some level a victim of their own success,” Offit said. “It just scares me that the only way we’re going to once again appreciate the importance of vaccines is to, at some level, experience some of these diseases again. I just wish we could do something to avoid that.”

What parents need to know

Vaccine preventable diseases can be deadly, which is why vaccines were developed to prevent them. Globally every year, 134,200 kids still die from measles, according to the CDC. The agency also estimates that failure to eradicate polio could cause poliovirus to reappear around the world with an estimated 150,000-200,000 new cases expected every year within 10 years.

“For all these diseases, there’s reasons that a lot of effort was made to develop these vaccines and deliver the vaccine. And for each individual one, I think it’s important for parents to know that if their kids are not vaccinated there are potentially very serious consequences,” Blumberg said.

Blumberg encourages healthcare providers to discuss the importance of vaccines and the consequences of not getting a child vaccinated as much as possible to parents and caregivers. “Lately, what I found is most useful is talking about each individual vaccine and talking about why it fits into the vaccine schedule, where it is, and what the consequences are of having children vulnerable to these vaccine preventable diseases,” Blumberg said.

Doctors also point out that a rate of 3% of immunizations exemptions still means 97% of kids in school are getting vaccines on time.

“The vast majority of parents are still vaccinating their kids according to the recommended schedule,” Dr. Sean O’Leary, chair of the American Academy of Pediatrics Committee on Infectious Diseases and professor of pediatrics at the University of Colorado Anschutz Medical Campus/Children’s Hospital Colorado, told ABC News.

O’Leary points out that while vaccines have been used as political tools in recent years, most parents care more about what their medical provider says than any politician. Talking to parents at health visits about the importance of vaccines is important.

“The vast majority of people really are not operating in the political arena, when they’re when they’re thinking about their own children,” O’Leary said. “[Parents are] operating in what is best for my child.”

Dr. Jade A Cobern, MD, MPH, is a board-certified pediatrician specialized in general preventive medicine and is a member of the ABC News Medical Unit.

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