Health and Human Services Secretary Tom Price was criticized this week for his seemingly limp enthusiasm about vaccines.

In an interview on CNN, Price was asked whether immunizations should be required for all Americans.

His response boiled down to: It’s up to states to enforce vaccine standards. “It’s a perfectly appropriate role for the government — this happens by and large at the state government, by the way, because they are the ones that have the public health responsibility — to determine whether or not immunizations are required for a community population,” he said.

HHS Secretary Tom Price says it should be up to states to regulate whether immunizations are required https://t.co/3QWUK3oy0W — CNN (@CNN) March 16, 2017

Some read this “less-than-rousing endorsement of mandatory immunization” as an “opening signal to the anti-vaccine movement.”

In truth, Price was just describing the status quo. Vaccinations do fall under the public health jurisdiction of the states. It’s up to them to set laws around who gets what shots when, and what kinds of exemptions are allowed.

Sure, Price could have been more forceful in underscoring the scientific consensus that universal vaccine coverage is ideal — especially at a time when the anti-vaccine movement seems to be emboldened under a president who’s been doubtful of vaccine safety. But the real missed opportunity here was to point out that states should be doing a much better job on vaccines. Some have loosened their standards over the years — and it’s helped spark a resurgence of preventable diseases.

The states that don’t have tough vaccine requirements see more people opting out of their shots

Several measles outbreaks in the 1960s spurred a push to have states require children get inoculated before starting school. By the 1980s, all states had mandatory immunization laws in place.

The idea behind these laws was simple: Near-universal vaccinations sustain what’s called “herd immunity.” For any vaccine to be effective and prevent outbreaks, a certain (high) percentage of people in a population need to be immunized. This keeps diseases from spreading easily, and keeps vulnerable groups that can't be vaccinated (such as very young babies or people with allergies to vaccines) protected.

But there’s a lot of variation across the country when it comes to immunization requirements. As of August 2016, all 50 states have legislation requiring vaccines for students — but almost every state allows exemptions for people with religious beliefs against immunizations, and 18 states grant philosophical exemptions for those opposed to vaccines because of personal or moral beliefs. (The exceptions are Mississippi, California, and West Virginia, which have the strictest vaccine laws in the nation, allowing no philosophical or religious exemptions.)

It turns out the parts of the country that make it easier for people to opt out of their shots tend to have higher rates of exemptions. In one paper, states that allowed parents to refuse vaccines for philosophical or personal reasons had exemption rates that were 2.54 times as high as states that only permitted religious exemptions. Another older study, looking at data between 1991 and 2004, found an increase in exemption rates only in states that allowed philosophical exemptions.

This 2009 New England Journal of Medicine paper, from Emory’s Saad Omer, is also instructive. Omer looked at the state-level rates of nonmedical exemptions. He finds that between 1991 and 2004, those rates increased from less than 0.98 percent to about 1.5 percent. Again, this uptick was not spread evenly across the US, and even varied within states.

Generally, though, states that allowed only religious exemptions had a steady opt-out rate of about 1 percent during the period (1991 to 2004). But in states that were more lax — allowing philosophical or personal belief exemptions as well as religious and medical exemptions — the mean exemption rate increased from 0.99 to 2.54 percent.

In another state-specific analysis, Baylor’s Peter Hotez looked at the rate of nonmedical exemptions over the past 13 years in his home state of Texas. He found that in 2016, there were almost 45,000 children who refused vaccines — about double the number of exemptions in 2010 and a 19-fold increase compared with 2003:

Texas is one of the states that allow parents to get both religious and philosophical vaccine exemptions.

Over time, the volume of people seeking exemptions has slowly crept upward across the US. Leah Samuel of Stat News crunched the latest Centers for Disease Control and Prevention data on nonmedical exemptions from 2009 to 2016 (her numbers, however, weren’t peer-reviewed, like some of the other studies I’ll describe next). She found that the number of people seeking exemptions was greater in 2016 than at any other point since 2009 in 11 states: Connecticut, Florida, Iowa, Kentucky, Maryland, New York, North Carolina, North Dakota, Ohio, Oklahoma, and Virginia. She also found the national average for nonmedical exemptions was down in 2016 from a 2009 spike — a fact she attributes to California and Vermont’s 2015 cancellation of their personal belief exemptions. So when states take a strong stance against exemptions, it can help tamp down the number of people who opt out.

States should pushback on vaccine exemptions

So we know that when state governments make it easier for parents to opt out of vaccines with different exemption provisions, they’re more likely to exercise that right.

We also know those exemptions are linked to upticks in preventable diseases. Measles and whooping cough, two infectious diseases US public health officials had gotten pretty good at preventing, have made a disturbing comeback in recent years, and researchers have found the outbreaks are closely tied to vaccine refusers.

So there’s a lot of room for improvement at the level of the states to toughen up on their vaccine requirements.

This 2014 JAMA paper offers a ray of hope. The researchers found that between 2009 and 2012, states considered 36 bills related to vaccine exemptions: 31 wanted to expand them, making it easier to opt out of vaccines, while only five wanted to make vaccine exemptions more difficult to obtain. None of the 31 anti-vaccine bills passed, while three of the five bills clamping down on vaccine deniers made it, which suggests that while there was more activity from the anti-vaccine side, public health won out in state legislatures. More states should go further, following the lead of Mississippi, California, and West Virginia by disallowing religious and philosophical exemptions.