California’s strict vaccination law will have only ‘modest’ impact, study says

California's tightened vaccination laws have pushed more parents to immunize their children.
(Mark Boster / Los Angeles Times)

Since California tightened its childhood vaccination laws in 2016, public health officials across the country have been closely watching for signs of success in bolstering vaccination rates.

A study published Monday offers an answer. In a brief in the Annals of Internal Medicine, researchers found that the strict law will have only a “modest” impact in increasing vaccination rates by 2027.

Supporters of the law, known as SB 277, contested the findings, pointing out that the law has already pushed up the state’s kindergarten vaccination rate to never-before-seen levels. SB 277 barred parents from citing their personal beliefs as a reason for not vaccinating their children and made California the third state in the nation to allow children to skip their shots only if they had a medical reason to do so.


Using state vaccination data, researchers projected that under SB 277, the percentage of children who would remain unvaccinated in 2027 because they are exempt from the law will be 1.87%. Without the law, researchers found, the percentage of kids exempt from vaccination requirements would have been 2.36%.

“The laws aren’t going to change people’s beliefs about vaccines,” said University of North Carolina geography professor Paul Delamater, the study’s lead author. “People who are truly opposed to vaccination are going to find a way to get around it if the law lets that happen.”

The study zooms in on what has often been missed in the conversation about the law’s success.

In the 2016-17 school year, the first year the law was in effect, the state’s kindergarten vaccination rate shot up from 92.8% to 95.6% — past the 95% threshold for preventing highly contagious diseases such as measles.

But only part of that increase was because of the implementation of the new law, according to state data. SB 277 contributed to a 1 percentage point increase in vaccination rates, while the rest of the jump came from a drop in students out of compliance with the law, state data show.

Each year, thousands of students are marked conditional entrants, meaning they begin the school year without all their required vaccines but are supposed to get them after the school year begins. An effort to bring more students in line with the vaccination schedule reduced the rate of students not in compliance with the law from 4.6% to 2.9% in the 2016-17 school year.


Delamater said the limited impact of SB 277 itself is a result of loopholes in the legislation, such as not requiring home-schooled students to be vaccinated and grandfathering in students who already had non-medical exemptions on file.

“There are these kind of compromises in the law that leave the door open,” he said.

An earlier Times analysis found that the number of kindergartners who were home-schooled and did not have their shots quadrupled in the state in the two years after the law took effect. Additionally, the number of children with medical exemptions has increased 70% in the past two years, a jump that some worry is driven by physicians increasingly penning fraudulent exemptions.

Sen. Richard Pan (D-Sacramento), who is an author of SB 277, said that though the law has not been bulletproof, the study understates its success.

The researchers calculated its effect by comparing the drop in exemptions under the law with a hypothetical scenario in which the exemption rate stayed fairly constant through 2027 — a highly unlikely possibility, he said.

Without SB 277, personal belief exemptions would have continued to increase, as they had for years, he said.

“To claim that without the laws things stay the same, I don’t know where that comes from,” Pan said. “That doesn’t comport with what was happening before, or in other parts of the country.”


Indeed, the trends highlighted by Delamater’s research show that such laws “will not achieve their full potential if they are not watertight,” but does not negate their effectiveness, wrote Stanford University health law professor Michelle Mello in an editorial published alongside the research brief.

Though SB 277’s effects may sound minimal, the drop in exemption rates across California will mean that tens of thousands more students will be up-to-date on their immunizations in 2027, she wrote. Plus, the regions with the lowest vaccination rates saw the greatest gains after SB 277 was implemented, making the effects even more significant, she said.

“To be dispirited about the prospects for legal reform to help improve immunization rates is an empirical mistake,” she wrote. “The devil, as Delamater and colleagues show, is in the details.”

Pan spearheaded an effort this year to further tighten California’s vaccination laws and crack down on fraudulent medical exemptions. Under a law known as SB 276, the state will gain the ability to review medical exemptions written by doctors who have given five or more waivers and at schools with an immunization rate below 95%.

Delamater’s team analyzed an earlier version of SB 276 that would have given the state the authority to review all medical exemptions written in the state, finding the state’s exemption rate would drop to 1.41% by 2027. He and others agreed the final version of the law will probably also reduce exemption rates.