Below, we’ve summarized the three recent studies that Delamater, Richwine and their colleagues authored. We also included other research we think you’ll find helpful, including a study that finds that the parents who were most likely to file personal belief exemptions before California banned them were white and from upper-income levels.
For journalists interested in comparing state laws on child vaccination requirements, the National Conference of State Legislators tracks which states allow medical and non-medical exemptions.
Associations of Statewide Legislative and Administrative Interventions With Vaccination Status Among Kindergartners in California Pingali, S. Cassandra; et al. JAMA, July 2019.
For this study, researchers examined the impact that three California initiatives — including Senate bill 277 — had on the vaccination rates of kindergarteners. In 2014, a new state law made it harder for parents to get a personal belief exemption. In 2015, school officials began limiting the number of children they allowed to start kindergarten on a conditional admission basis. Then, in 2016, Senate bill 277 was enacted, eliminating personal belief exemptions.
The researchers find that between 2000 and 2017, 9.3 million California kids entered kindergarten, 721,593 of whom were not up to date on their required vaccinations. During the period the three initiatives were launched, the percentage of kindergarteners with incomplete vaccinations fell. In 2013, 9.84% of kindergarteners were missing some or all school-mandated immunizations. That number dropped to 4.42% in 2016 but then rose slightly to 4.87% in 2017.
Most of the reduction in kindergarteners with incomplete vaccinations is linked to the crackdown on conditional admissions, the rate for which dropped from 6.5% in 2013 to 1.84% in 2017, find the researchers, led by S. Cassandra Pingali, a fellow in the Immunization Services Division of the U.S. Centers for Disease Control and Prevention. Meanwhile, the slight increase in 2017 is related to the rising number of children using medical exemptions and a jump in the number of kindergarteners who are overdue for vaccinations. Senate bill 277 also allowed 5,310 kindergarteners in 2017 to forgo vaccinations s if they attended a school without classroom-based instruction or had individualized education plans.
The authors find that California communities reacted differently to the three interventions. In 2016 and 2017, reductions in the share of kindergarteners with incomplete vaccinations appear to be largest in the southern part of the state. “Northern California maintained the highest predicted rate of students without up-to-date vaccination status throughout the study period with relatively minor changes during the implementation of the 3 interventions compared with the rest of the state,” the authors write.
Elimination of Nonmedical Immunization Exemptions in California and School-Entry Vaccine Status
Delamater, Paul L.; et al. Pediatrics, June 2019.
This study looks at Senate Bill 277’s effect on the percentage of California students entering kindergarten with incomplete vaccinations. A key takeaway: While the percentage of kindergarteners whose vaccinations were not up to date fell during the first year of the law, it rose in the second year.
Researchers tracked three categories of children who had not received all school-mandated vaccinations: those who were allowed to start kindergarten as conditional entrants, students who were overdue to receive one or more vaccinations and those who were “exempt” because they either attend a school without classroom-based instruction or have individualized education plans.
The researchers find that the percentage of kindergartners starting school not up to date on their vaccinations fell from 7.15% to 4.42% during the first year after Senate Bill 277 was enacted. But much of this drop was due to a reduction in the number of children who entered kindergarten on a conditional basis, the researchers note. The conditional entrance rate fell from 4.43% to 1.91% in 2016. In the second year after the law took effect, the percentage of kindergartners who weren’t up to date on their vaccinations increased by 0.45%.
It appears that personal belief exemptions “were replaced by other mechanisms allowing kindergarteners not up-to-date on vaccinations to enter school,” writes the research team, led by Delamater.
“Some parents who would have claimed a personal belief exemption before SB277 may have initiated the series of vaccines to meet the requirements for conditional entrance after the law’s implementation,” the authors write. “Yet, data reporting progression toward series completion are not available and we are not able to know whether or when students became fully up-to-date on vaccinations.”
The authors also find that many of the parents who sent their children to school with incomplete vaccinations after Senate Bill 277 was enacted lived in the same geographical areas where many parents previously had filed personal belief exemptions. “Previous geographic patterns of vaccine refusal persisted after the law’s implementation,” the authors write.
Do Stricter Immunization Laws Improve Coverage? Evidence from the Repeal of Non-medical Exemptions for School Mandated Vaccines
Richwine, Chelsea; Dor, Avi; Moghtaderi; Ali. Working paper for the National Bureau of Economic Research, May 2019.
While other studies established a relationship between California Senate Bill 277 and higher childhood vaccination rates, this study finds that the new rule actually caused California vaccination rates to improve. This study also differs from others by examining changes in vaccination rates for each of the four vaccines required for kindergarten. The three researchers — Richwine, Avi Dor and Ali Moghtaderi of George Washington University — find that vaccination rates rose among all four vaccines in California, ranging from an increase of 2.5% for the measles, mumps and rubella (MMR) vaccine to an increase of 5% for the polio vaccine.
As part of their analysis, Richwine, Dor and Moghtaderi looked at parents’ use of personal belief exemptions and medical exemptions in California before and after Senate Bill 277 was enacted and compared it to parents’ use of these exemptions in seven control states — Arizona, California, Connecticut, Kansas, Minnesota, Pennsylvania and Rhode Island. What they learned is this: Compared to control states, California had lower vaccination rates and higher rates of students using personal belief exemptions in 2015, the year before the legislation took effect. After California banned personal belief exemptions, the rate of students using them there fell below that of the control states. However, California also “experienced a sharp increase in medical exemptions while control states’ exemption rates remained unchanged.”
Richwine, Dor and Moghtaderi find that California’s policy change reduced the rate at which children used personal belief exemptions by 3.4 percentage points. But that drop was offset by “a significant 2 percentage-point increase in medical exemptions in several of our analyses, which limits the overall decline in total exemptions to just 1 percentage-point.”
Sociodemographic Predictors of Vaccination Exemptions on the Basis of Personal Belief in California
Yang, Y. Tony; et al. American Journal of Public Health, January 2016.
This study’s main finding: White, upper-income parents were most likely to seek personal belief exemptions in California before the state banned them. The research team — led by Y. Tony Yang, currently executive director of George Washington University’s Center for Health Policy and Media Engagement — analyzed millions of kindergarteners’ vaccination data to identify where in the state personal belief exemptions were most prevalent. The team combined vaccination data from the 2007-08 to 2013-14 academic years with data from the U.S. Census Bureau’s 2008–2012 American Community Survey to better understand the characteristics of families who used these exemptions.
The researchers find that the percentage of California kindergartners who used personal belief exemptions to forgo vaccinations rose from 1.54% in 2007-08 to 3.06% in 2013-14. The share of private school students using these exemptions was almost twice as high as the share of children using them in public schools.
Yang and his colleagues also find that the “areas of California with higher household income and proportion White population are associated with higher overall PBE [personal belief exemption] percentages as well as greater increases in PBEs [personal belief exemptions].”
“An increase in percentage White population from 20% to 35% yielded 1 additional PBE [personal belief exemption] per 280 students in 2013, and an increase from 65% to 80% yielded 1 additional PBE [personal belief exemption] per 139 students,” they write.
Parent Psychology and the Decision to Delay Childhood Vaccination
Callaghan, Timothy; et al. Social Science & Medicine, July 2019.
For this study, researchers analyzed data collected through a national, online survey to better understand why some families delay childhood vaccinations. A total of 7,019 U.S. adults responded to the September 2018 survey, 31% of whom were parents with children under age 18 living at home. The parents answered a series of questions about childhood vaccinations.
Researchers find that parents with high levels of “conspiratorial thinking” and those uncomfortable with needles were more likely to say they have followed a vaccination schedule that differs from what’s recommended by the CDC. Parents with high levels of conspiratorial thinking agreed with statements such as “Even though we live in a democracy, a few people will always run things anyway” and “Much of our lives are being controlled by plots hatched in secret places.”
“Compared to those who scored lowest on conspiratorial thinking, those who scored highest were 15% more likely to report having delayed vaccinating their children, 11% more likely to have chosen their doctors based on their willingness to delay, 25% more likely to have only vaccinated their children for schools, and 18% more likely to state that they would be willing to relocate in order to attend a school that does not strictly enforce vaccination requirements,” write the authors, led by Timothy Callaghan, an assistant professor of health policy and management at Texas A&M University.
The authors also find that “individuals most sensitive to needles are between 14 and 16% more likely than those without sensitivity to display [vaccine] hesitant behavior.” The analysis also indicates “fathers are more likely than mothers to display many vaccine delay behaviors.”
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