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Immunization rates vary heavily from state to state and by individual vaccine, with the national average hovering in the low nineties (most health professionals agree that a 95% or better immunization rate is optimal). First let’s talk about that 95% statistic and why it’s necessary to have so much of the population immunized.

Herd immunity is how we protect our communities from vaccine-preventable infectious disease. If most members of a community are immunized, it’s unlikely that an infectious disease in one person will spread throughout the rest of the community.

We consider a 95% immunization rate optimal based on rates of contagion of the measles virus, the most contagious of vaccine-preventable illnesses. Not all infectious diseases are as contagious as the measles virus: for example, only an 80% vaccination rate is necessary to adequately protect communities against poliomyelitis. This is especially concerning because the MMR vaccine, which immunizes the recipient against measles, has become increasingly less popular in recent years, meaning that in communities with vaccination rates below 95%, measles outbreaks are becoming increasingly likely.

There have been two Supreme Court cases that have established the United State’s legal doctrine regarding vaccinations: Jacobson v. Massachusetts (1905) and Zucht v. King (1922). These cases allowed for the state to directly mandate vaccination or to delegate that authority to local boards of health, respectively. These cases give states the authority to enforce statewide vaccination mandates for anyone without a medical exemption, as long as their mandates do not target specific groups or persons.

The national vaccination rate, while not optimal, is good. However, state vaccination rates vary by about 18% from extreme to extreme. To investigate the possible reasons for these divisions, let’s take a closer look at the American states with the most extreme vaccination rates: Colorado with the lowest, and Mississippi with the highest.

That’s right! Mississippi, with 99.9% of Kindergarteners currently immunized on schedule, has the nation’s highest vaccination rate. Since 2008, Mississippi has not experienced a single recorded case of vaccine-preventable illness. Mississippi’s vaccination rates are so high because they only allow medical exemptions to vaccines – religious and philosophical exemptions are not permitted, including in private schools. This is largely due to a 1979 Mississippi Supreme Court case which ruled that religious exemption to vaccination is unconstitutional on the basis of the exemption violating the equal protection clause of the 14th amendment.

Weld County, Colorado, and the town of Windsor in particular, have been hard-hit by pertussis outbreaks in the local public schools, with 116 cases in 2013 alone. Windsor schools have better vaccination rates than the state as a whole, but with an 8% exemption rate, there is major room for improvement. So, why does Weld County experience so many cases of vaccine-preventable illness if it has vaccination rates that are apparently higher than most of the state? For one, the statistics given on vaccination rates in Windsor schools exclude Windsor Charter School, which likely has an extremely low vaccination rate. It could also be the case that pertussis vaccine has a disproportionately low compliance rate in comparison to other vaccines (pertussis vaccination rates are generally much lower than those for other vaccines across the country).

McMeen Elementary in Denver has immunization statistics that are typical of the Denver public school system. McMeen has a low exemption rate – just 1.30% – but a low compliance rate as well, with 86.10% of students fully immunized or officially exempted. This makes McMeen’s actual vaccination rate ambiguous, as the compliance rate only implies how many students are fulfilling their exemption status or lack thereof.

Tope Elementary School in Grand Junction shows an entirely different side of Colorado and immunization. The school has an exemption rate of 2.6% and a 100% compliance rate, making an immunization rate of 98.4%. But why are Tope Elementary’s rates so much better than the majority of Colorado schools? Firstly, Grand Junction is a very different area demographically than Denver, where vaccination rates are generally low. Grand Junction has a lower median income and a higher poverty rate than average for Colorado, as well as a higher minority population. Additionally, almost 20% of Grand Junction’s population has no health insurance – but this doesn’t seem to have a negative effect on its immunization rate.

It may not seem as though median income should have anything to do with immunization rates, but evidence suggests that it does. With few exceptions, states with the lowest vaccination rates are richer, and those with the highest are poorer. Tope Elementary suggests that this trend is also consistent within states as well as between them.

Mountain Phoenix Community School, located in Wheat Ridge, a Denver suburb, is a Waldorf-inspired charter school. 37.07% of Mountain Phoenix students have claimed exemptions to immunizations of some kind, but only 47.76% comply with these exemptions or lack thereof. This implies an immunization rate of between about 30% and 63%. Mountain Phoenix’s immunization rates are dangerously low, but are not unique for Colorado charter schools, most of which have vaccination rates below 80% and often below 70%.

Statistics and policy suggest that charter schools have a large influence on Colorado’s immunization rates. There are more limitations when it comes to creating charter schools in Mississippi, although these have lightened since 2013. Colorado’s public school systems generally have poor vaccination rates, but charter schools have rates that are disproportionately low even within the state. The immunization rate for Mountain Phoenix Community School, for example, means that a single instance of vaccine-preventable illness in the school would almost certainly lead to a widespread outbreak there.

As we saw with the case of McMeen Elementary in Denver, many Colorado schools have low exemption rates, but low compliance rates, making their actual immunity ambiguous. South High School in Pueblo exhibits the opposite case: a high exemption rate at 20.75%, and a high compliance rate of 99.92%. Therefore, we know South High’s immunization rate is about 80%. South High’s compliance and exemption rates represent the opposite but equally concerning trend than many Colorado schools. Interestingly, Pueblo city is poorer than Grand Junction and has a much higher minority population as well as a lower rate of health insurance. However, it appears that South High School is located in a more affluent area of the city.

The reasons behind American disparities in immunization rates are many and complex, but a few of them may be visible in the data provided. For one, vaccination rates have an inverse correlation with income. This may be because vaccination is one of the cheapest, easiest, and most available forms of protection against disease, which is expensive to treat once present. Immunization rates are also dependent on personal ideology, which is impossible to measure without extensive personal interviews and other data. Education laws take part as well, with Colorado’s lenient charter and private school laws which make the creation of these schools much easier than in Mississippi.

References

Blinder, Alan. “Mississippi, a Vaccination Leader, Stands by Its Strict Rules.”The New York Times International. The New York Times, 04 Feb. 2015. Web. 16 Apr. 2015.

Bluemel, Allison Dyer. “Windsor, Weld Schools’ Vaccination Compliance Rates Remain Steady” My Windsor Now. 14 Feb. 2015. Web. 4 Apr. 2015.

 “Charter Schools.” Mississippi First. Mississippi First, 2015. Web. 30 Apr. 2015.