Who Are California’s Anti-Vaxxers?
An Investigation of California Kindergarten Immunization Data (2000–2015)
My colleague Allison Godfrey and I completed a study of kindergarten immunizations in California in the spring of 2020. It was just a few weeks after the COVID-19 pandemic had begun to have widespread impact in the US, and many months before the first COVID-19 vaccine became available in December 2020. We didn’t know then if there would ever be a COVID-19 vaccine, and like so many others, I hoped that strict lockdown and constant handwashing would end the pandemic long before vaccination became necessary. But after more than a year of catastrophic suffering and death due to COVID-19, it is clear that the COVID-19 vaccines are our best hope for a return to “normal” life.
Pfizer’s COVID-19 vaccine is currently available to all Americans age 12 and older. At the time of publication (June 2021), children under 12 are still ineligible; clinical trials are currently underway to determine safety and efficacy for children as young as six months. However, the pro/anti-vaccination debate among parents is already raging, and it will likely only intensify when the vaccine becomes available for younger children. A Harris poll conducted June 11–13 among 2,015 US adults found that 27% of parents of children under 12 say they will not get their children vaccinated, and a further 11% say they will only have their children receive one of the two recommended doses. Their reasons include wanting to wait for more research on the vaccines’ effects on children, not believing COVID-19 is serious enough in children to warrant vaccination, and general anti-vaccine sentiment.
It is too soon to know for certain, but it seems likely that the same parents who have refused the Measles/Mumps/Rubella (MMR) and Diptheria/Tetanus/Pertussis (DTP) vaccines for their kindergarteners will refuse the COVID-19 vaccine on their behalf as well. In this analysis, we strive to understand who they are and provide insights into how to reach them.
A Short Recent History of Vaccine Hesitancy
Vaccinations provide people the ability to develop immunity to particular diseases. When the majority of a population is vaccinated, herd immunity protects those who have not been vaccinated by blocking the spread of these diseases. However, the 21st century has seen worldwide concern over the safety of the MMR vaccine and other types of vaccines — despite the lack of scientific evidence to substantiate these fears.
This trend has been called vaccine hesitancy, anti-vaccination, or “anti-vax” for short. Anti-vax refers to a refusal or reluctance to have children vaccinated despite the overwhelming evidence that vaccines are safe and effective. This hesitancy may come from a misunderstanding of the ingredients in vaccines and how they work, mistrust of doctors and pharmaceutical companies, and/or belief in the unfounded associations of vaccines with other diseases and disorders such as autism.
Anti-vaccination was identified by the World Health Organization as one of the top ten global health threats of 2019. In California, an alarming 15-year-long anti-vax trend starting in 2000 led to Senate Bill 277, signed into law in 2015, which eliminated Personal Belief Exemptions for vaccinations of school-age children. California is currently one of only three states in the US with such a law.
A Few Notes on Terminology
Throughout this analysis, “vaccination rate” refers to the average kindergarten vaccination rate for the MMR and DTP vaccines, unless noted otherwise. The rates for other vaccines, including polio, chickenpox, and seasonal flu, are not included.
Vaccination is important not only to protect the individual from disease, but also to protect their community through herd immunity. Therefore, for this analysis, we define low, middle, and high vaccination communities based on their average vaccination rate relative to the estimated Herd Immunity Thresholds (HITs) for measles and pertussis (92%-95%). “Low-vax” is defined as less than 92% vaccinated, “high-vax” is over 95% vaccinated, and “middle-vax” is in between. In 2008, eight of California’s 58 counties fell below the 92% vaccination rate. In 2015, there were 23.
Where did they live?
In every year between 2000 and 2015, low-vax communities were largely concentrated in the regions and counties of the northern half of the state.
The average vaccination rate across all counties steadily declined from 2000 to 2013, dropping 2 percentage points below the minimum estimated HIT for measles and pertussis statewide. There was a slight uptick in the overall average vaccination rate beginning in 2013, reaching 93% in 2015, moving the state average from low-vax to middle-vax.
All of the 23 low-vax counties in 2015 had lower vaccination rates than they did in 2000. Trinity, Nevada, Humboldt, and Mariposa Counties had the largest declines during that period. Nevada County, a small, sparsely-populated county in the northeastern part of the state, had the lowest annual vaccination rate of any county in any year (70% in 2012, down 19 percentage points from its 2000 rate of 89%). However, because the county is so small, this equated to only about 250 unvaccinated kindergarteners, far fewer than in larger counties with higher vaccination rates.
Where did they go to school?
Low-vax schools were located throughout the state, even in large counties that were high-vax on average such as San Francisco, Santa Clara, Los Angeles, and San Diego Counties.
For both vaccination types, the average state-level vaccination rate of private schools was below the minimum measles/pertussis HIT of 92%, while that of public schools was above the threshold.
However, despite lower rates of vaccination in private schools, the absolute number of unvaccinated kindergartners was much greater in public schools because these schools were both larger and more numerous (approximately 406,000 unvaccinated kindergartners in public schools versus 69,000 in private schools over the 15 year period).
Small schools — for this analysis defined as those with fewer than 18 kindergartners — tended to have much lower vaccination rates than larger schools. This held true for both public and private schools.
Waldorf Schools
Waldorf education, a progressive educational model founded in post-WWI Germany, is based on the philosophy of Rudolf Steiner and strives to develop students’ intellectual, artistic, and practical skills in an integrated and holistic manner. Steiner opposed childhood vaccinations when they first became available in the early 20th century, writing that they could “impede spiritual development”. He taught that diseases were influenced by “astral bodies”, rosemary baths could cure diphtheria, and smallpox could be avoided by mental preparation.
Over the last two decades, private Waldorf schools throughout the United States and other countries have been reported to have unusually high rates of vaccine exemption, even compared to other specialized private schools, and have had a spate of disease outbreaks. From 2000 to 2015, Waldorf schools in California had the lowest average vaccination rates of any school sub-type at 44%. Every private Waldorf school in California failed to reach the minimum HIT for measles and pertussis in every year from 2000 through 2015.
How were they alike?
Based on 2010 US Census data, California’s 19 low-vax counties in that year shared similar characteristics in race and education: almost all had much whiter populations and more high school graduates than the state average. In regression analysis, low vaccination rates had a highly statistically significant relationship with larger populations of white people and high school graduates.
Sacramento County, a populous county in the Central Valley that includes the state capital city of Sacramento, was the only low-vax county in 2010 that did not fit this demographic profile. Although its share of high school graduates at 87% was higher than the state average, its white population at 60% was slightly lower; only six counties in the state were less white.
All of the low-vax counties were less populous than the average county population across the state except Sacramento County. However, many other counties with small populations had high vaccination rates.
How were they different?
In 2010, the counties with the lowest vaccination rates in the state varied in median income and politics.
Low-vax counties included both Trinity County, with the lowest median household income in the state at about $38.5K, and Marin County, with the third-highest at more than $110K. 15 of the 19 low-vax counties had lower median incomes than the average, but many other lower-income counties had middle or high vaccination levels, disproving the idea that low vaccination rates are directly correlated with low income. This also suggests that low vaccination rates may not be associated with less access to or lower quality of health care services.
Based on the difference between registered Democrats and registered Republicans, 13 of the 19 low-vax counties were Republican-leaning, while 6 were Democratic-leaning. The middle- and high-vax counties are also well-distributed across the political spectrum, including both the most Republican and most Democratic counties in the state (Modoc and San Francisco, respectively).
Three low-vax counties (Marin, Sonoma, and Santa Cruz) are both higher-income and Democratic-leaning; all three are also coastal counties in the greater San Francisco Bay Area. 13 low-vax counties are both lower-income and Republican-leaning; these counties are mostly inland. Only three low-vax counties have other combinations of income and politics (Humboldt and Mendocino, which are lower-income and Democratic-leaning, and El Dorado, which is higher-income and Republican-leaning). This suggests that there are at least two distinct groups of anti-vaxxers who may have come to their views on vaccination independent of each other, despite their similar behavior regarding vaccinations.
Why didn’t they vaccinate?
From 2000 to 2015, many anti-vaxxers cited personal beliefs as their reason not to vaccinate their children. Medical reasons made up a much smaller share of exemptions during this time period.
Many non-vaccinations were unexplained by either type of exemption. These included conditional entrants who were required to receive immunizations after entry; students in home-based private schools, public independent study programs, and individualized education programs (IEPs); and students who were overdue for vaccinations and excluded from school until they received them.
What was their impact?
In California, steadily declining vaccination rates coincided with the largest pertussis outbreak in more than 60 years in 2010, followed by an even more severe outbreak in 2014. Reduced vaccination frequency was also linked to a high-profile measles outbreak that began at Disneyland in late 2014. In response, the California Legislature passed Senate Bill 277, effective July 2016, which eliminated Personal Belief Exemptions (PBEs), making it much more difficult for parents to opt out of vaccinations for their children.
SB 277 led to a dramatic increase in the vaccination rate that year. However, in the years since, the rates have begun to decline again. At the same time, Permanent Medical Exemptions (PMEs) have increased substantially, up 450% from 2015 to 2018. Since it is unlikely that so many children have suddenly become too sick to be vaccinated, it is more likely this trend indicates the increased willingness of some doctors to issue PMEs even when not medically warranted.
In 2019, SB 276 and 714 were signed into law despite fierce opposition by anti-vaxxers, creating state oversight of medical exemptions for vaccines. 2019 also saw the US’s worst measles outbreak in more than 20 years, with more than 1,200 people diagnosed across 31 states, including California.
Why does it matter?
Vaccines are the best way to put an end to the serious effects of the diseases for which we are fortunate enough to have them. But when we stop vaccinating our children, diseases that are almost eradicated come roaring back. In the 21st century in the US we have seen many epidemics of pertussis and measles, two diseases that were nearly eliminated at the end of the last century. Because of this, more children have gotten sick and more children have died than ever should have had to.
According to the World Health Organization, vaccination resulted in a 73% drop in worldwide measles deaths between 2000 and 2018, preventing an estimated 23.3 million deaths. Even so, measles infections were responsible for more than 140,000 deaths globally in 2018 alone. Most of them were children under the age of five.
And we don’t vaccinate just to protect today’s children; we also vaccinate to protect future generations. With one disease, smallpox, we “stopped the leak” in the boat by eradicating the disease through vaccination. Children today don’t have to get smallpox shots because the disease no longer exists.
In the context of the COVID-19 pandemic, vaccination has taken on an immediacy and urgency that many did not previously feel. Very few Americans alive today have been personally affected by smallpox, polio, measles, pertussis, or any of the other childhood diseases that we can vaccinate against. But every American has felt the impact of COVID-19 in some way, even if they themselves have not contracted it. As of June 16, 2021, almost 53% have received at least one dose of a COVID-19 vaccine — enough to allow schools and businesses to reopen, but not enough to reach herd immunity. Through vaccination, we have the power to end the pandemic. Smallpox is now only a memory, and if we keep vaccinating against COVID-19, the same could someday be true for it too.
This project was created with Allison Godfrey in the Master of Information and Data Science program at the UC Berkeley School of Information using Kaggle’s California Kindergarten Immunization Rates dataset.
