The History of Vaccines and the Importance of Vaccine Mandates

Part 5: Measles Vaccines and the Importance of School Mandates Today

(This post is based upon data collection and the 2024 Fordham University undergraduate thesis of Robert Betancourt. Opinion on the elimination on non-medical vaccine exemptions is mine.)

On November 5, 2022, two toddlers were admitted to an Ohio hospital and diagnosed with measles. These cases started an outbreak that resulted in 85 measles cases, 36 hospitalizations, and 739 documented exposures of unvaccinated people. These cases and exposures impacted four childcare centers and five healthcare facilities in the area. 

While this was a somewhat larger than normal measles outbreak, similar events are becoming more common across the US. In 2024 to date, there have been cases in 29 states and 13 outbreaks have occurred. (The CDC defines an outbreak as three or more related cases.) Cases also have spiked recently. In 2019, 1,274 cases of measles were reported in the U.S. This was the largest number of cases since 1992. Many think measles is a relic of the past or that it is a mild disease that is little more than an annoyance for infected children. However, in 2024, 43 percent of measles cases in the U.S. have resulted in hospitalization. The hospitalization rate for children under five years old is 55 percent. More broadly, across the world, over 100,000 people die from measles every year.

Why do measles cases appear to be on the rise in the U.S.?  In part the increase is due to a decrease in overall vaccination rates in recent years. However, this is not the primary cause of the increase in outbreaks. Instead the pattern of vaccinations across geographic space plays a much larger role than the relatively small decrease in overall vaccination rates. Children whose parents choose not to vaccinate them tend to be clustered into the same schools, childcare centers, and geographic areas. When a random case lands in one of these clusters it is likely to spread to other unvaccinated children resulting in one of the outbreaks that occur more and more frequently in recent years. Just like the example of polio vaccine not reaching urban centers that I discussed in part 4 of this series, the clustered distribution of unvaccinated people makes it more likely that cases spread widely once a single case occurs.  

Why do we observe this clustering of unvaccinated children? Most states require a variety of vaccinations for children attending schools and childcare centers, most notably the measles, mumps, and rubella vaccine (MMR). Many states also grant exemptions to vaccine requirements for religious or personal belief (in addition to medical conditions). Many states currently face controversy over these exemptions and some states are considering expanding access to exemptions or allowing more lenient conditions to receive an exemption.

At the start of the 2022-2023 school year, vaccine exemptions for school children in the United States reached an all-time high (data for more recent school years is not yet available). In 2022-2023, three percent of children were exempt from at least one state vaccine requirement because of a request by parents that was granted by a school district. A November 2023 Centers for Disease Control and Prevention (CDC) report highlighted this increase as a worsening public health problem. The increase in exemptions contributed to MMR vaccination rates decreasing by about two percent over the previous two years.

To many, this decrease may seem relatively minor. However, looking more deeply into the distribution of these vaccine exemptions across schools reveals even more danger than one expects from this small decrease in vaccine coverage. These vaccine exemptions tend to be clustered in a subset of specific schools (most prominently private schools) and geographic areas. This clustering of unvaccinated children leaves some communities at extreme risk of widespread outbreaks like the one that occurred in Ohio. 

Consider data from California that was collected by current Cornell University Ph.D. student Robert Betancourt. (Robert is a former undergraduate student of mine at Fordham.) In 2001, only 0.7 percent of entering kindergarten students in California had an MMR vaccine belief exemption. By 2014, 3.2 percent of entering kindergarteners had been granted a belief exemption. During this same time period, overall vaccination rates fell from 95.5 percent to 92.3 percent. While this decrease is concerning, underlying this data are far more alarming patterns of divergent vaccine behavior within specific schools, particularly private schools.

In 2014, 20 percent of California private schools had at least 20 percent of their kindergarteners unvaccinated for MMR. Further 11 percent of private schools had at least 30 percent of their kindergarteners unvaccinated for MMR.  Almost all of these children were unvaccinated because of belief exemptions. (Similar unevenness occurred in public schools but to a smaller extent.) These schools with such drastically low vaccination rates were at risk of turning the spark of a single case into an epidemic inferno.

One might be inclined to argue that families should have the choice to forego vaccines for their children. Yet, non-medical exemptions place risk onto others. First, some children cannot be vaccinated for medical reasons and others are too young to receive the MMR vaccine (first dose recommended at 12-15 months of age and second dose at four to six years). These young children and the children with medical conditions trust that the vaccinations of others will keep them safe by limiting the risk of an outbreak. In the Ohio outbreak that started this post, 25 of the 85 cases occurred in children too young to receive their first vaccine dose. Second, some unvaccinated children have parents who lack access to high quality health-care, have limited financial means, and cannot make regular medical appointments for their children who then fall behind on recommended vaccinations. Exemptions place these innocent children at risk because of their socio-economic disadvantage. 

Putting all of this together, we can see the danger of the clustering of these non-medical vaccine exemptions, that the American Academy of Pediatrics has argued should be eliminated.  In 2014, California did exactly this (although the change didn’t take full effect until 2016). What was the result? A far more even distribution of vaccines across schools and less risk for all children.

After eliminating exemptions, by 2019, only 2 percent of private schools in California had MMR kindergarten vaccine coverage of less than 70 percent (compared to 11 percent in 2014), and only 5 percent of private schools had less than 80 percent coverage (compared to 20 percent in 2014). In 2019, vaccine coverage levels were distributed more evenly than in 2001 when this data were first collected.

By eliminating non-medical vaccine exemptions, California reversed a two decade trend in one fell swoop. Eliminating these exemptions not only increased overall vaccination rates but also eliminated many of the geographic pockets of extreme danger. In doing so, California created a more equitable and safe environment for all children in the state. It is time for more states to follow their lead and eliminate non-medical vaccine exemptions.

Troy Tassier is a professor of economics at Fordham University and the author of  The Rich Flee and the Poor Take the Bus: How Our Unequal Society Fails Us during Outbreaks.

Part 1: Asia: The Earliest Inoculations

Part 2: Inoculation in the North American colonies and Washington’s mandate

Part 3: A Safer Procedure and the Rise of New Vaccinations

Part 4: Vaccine Inequality and the Case of Polio

Part 5: Measles Vaccines and the Importance of School Mandates Today