Immunization Rates and Current Cases

In spite of the efficacy of the MMR vaccine, parents in the United States are increasingly electing not to vaccinate their children. This, in turn, lowers “herd immunity,” the immunization coverage threshold at which a population is indirectly protected from disease, putting unvaccinated children and immunocompromised individuals at risk. Herd immunity against measles is attained when 93-95% of a population is vaccinated (for the purposes of this project, it was set to 94%).

In December 2018, cases of measles began to rise as international travelers exposed to the disease abroad came in contact with disease-vulnerable populations. As of mid-April, cases occurred in 22 states and outbreaks (higher than normal case counts) were reported in six states, California, Michigan, New Jersey, New York, Oregon, and Michigan. Cases affiliated with these outbreaks are depicted at the county level in the map below.

The most active outbreaks as of mid-April were recorded in California, New York, Oregon, and Washington. Immunization coverage levels and case counts (as reported to the National Notifiable Diseases Surveillance System) are compared below to see how these figures have varied in recent years across the four states.

The most recent immunization coverage data from the CDC is current to 2017 and reveals that in each of these four states, herd immunity against measles has rarely been achieved in recent years.

Measles cases in California, New York, Oregon, and Washington spanning the same time period to mid-April 2019 are given below.

The 2019 measles cases in New York are particularly striking. The number of cases reported in New York in 2019 is nearly on par with that from 2018, despite the fact that the data for 2019 only includes the first three and a half months of the year.

What are people in New York saying?

As measles cases have spread in the United States, so has the online dicussion surrounding the condition. We analyzed measles-related Google search terms and tweets, first to identify trends over time and top concerns, then to compare how pro- versus anti-vaccination opinions differ.
Spikes in Google searches for measles by New York residents parallel outbreaks. The two large spikes in searches for measles symptoms coincide with the 2015 California outbreak and the current outbreaks. The spikes suggest New York residents are concerned. They want to either be educated on measles symptoms since there is a risk in their community or they are concerned they or someone they know is exhibiting these symptoms. Either way, the spike indicates that New Yorkers believe they are at risk.

On Twitter, the most common term associated with the #measles hashtag in New York in the immediate weeks after the public health emergency declaration, aside from the disease itself, was vaccination. This top term hints at the controversy that, in part, is fueling the current outbreak’s spread. The most popular terms indicate a call to action to vaccinate with the overall message that vaccines work.

Words commonly associated with the #measles are also visualized through a wordcloud below.

The most frequent terms in tweets from anti-vaxxers are highlighted in red, while top terms from a pro-vaccine point of view are featured in blue. The hashtags used to identify anti-vaxxers were #VaccineInjury, #VaccineFailure, #VaccineHarm, and #VaccinesCauseAutism. The hashtags used to identify pro-vaxxers were #VaccinesWork and #GetVax. Both sides utilize an emotional plea, one being that vaccines pose a risk of injury and autism to those receiving it, as well as overall failure. The pro-vaccines side pleads that vaccines work and protect, citing organizations such as UNICEF and the Gates Foundation.

Identifying Trends Over Time

Over time we see that while the average medical exemption rate has remained consistent at about 0.25%, the average religious exemption rate is increasing. In 2018, this rate was 3.77%.

Average Immunization Rates by Counties

Below, average measles immunization rates are mapped by county.

We then identify the counties that have immunization rates less than 94%, again as this is the benchmark for successfully establishing herd immunity. There are 15 counties that meet this criteria. The bar chart below depicts these 15 counties at risk of measles contagion.

The top 5 counties in New York with the lowest measles vaccination rates are Montgomery, Yates, Allegany, Cattaraugus, and Seneca.

The interactive map below shows the schools in New York that have immunization rates below the ideal threshold needed to achieve herd immunity. We have identified 574 schools as being risky.

Type of Risky Schools

Among those schools identified as at risk of becoming a location where measles can spread, the most common type of school is private schools. Private schools are subject to fewer government regulations and statutes than public schools, particularly when it comes to mandatory immunization.

Text Analysis of Risky Schools

“Christian” is the most frequent term among the risky schools’ names.

Following “christian”, words associated with schools that have low immunization rates include “yeshiva” and “montessori,” referring to relgious and alternative learning institutions.

Text Analysis of Riskiest Schools

Of the 574 risky schools with below-threshold immunization rates, there are 91 where no child is vaccinated against measles.

Most frequent 2-grams in school names

Again, we see references to religious instituions through words like “muhammed”, “menonite”, and “amish” in the 91 school names.

Focusing on New York City

There are 104 schools in the New York City ‘at-risk’ category. Every school below the 94% immunization threshold in NYC is a private school. These are first reviewed through a static plot.

We then compare the medical exemption and the religious exemption rates between NYC boroughs.

Examining 2019 Measles Mandate

Under the NYC Measles Mandate, requiring residents of the identified areas to receive the MMR vaccine except when immunity or medical exception can be proved, four zip codes will be affected: 11205, 11206, 11211 and 11249. These zip codes are geographically close to centers of measles outbreaks. However, in a densely populated city with a well-frequented public transit system, a highly contagious disease like measles can spread across boroughs.

The health mandate covers only 44 schools, whereas we have identifed 104 schools in New York City that are at risk of a measles outbreak. We then perform a text analysis on the school names to see what patterns emerge.

The resulting most frequent terms are very interesting because we previously saw that “christian”" was the most frequent word in the risky dataset in New York State. In contrast, the schools covered under the mandate are primarily Jewish Orthodox insititutions.

The barchart shows that many of the identified schools are well above the threshold for herd immunity.

In fact, more than half of the schools in the zip codes identified by the NYC Health Department have vaccination rates that are adequate for herd immunity (25 schools).

Using Data to Improve NYC Policy

Let’s look at average measles immunization rates by zip codes

Zip Code	Average Immunization Rate
10026	47.60000
11221	75.05000
11237	75.80000
10001	85.20000
10038	85.70000
103143205	90.90000
10009	91.26667
11238	91.35000
11206	92.28571
11211	92.28636
11216	92.40000
10030	92.90000
11213	93.07692
10309	93.50000
10454	93.80000

Only 2 zip codes in the list above (i.e. 11221 and 11206), were correctly identified by the NYC Health Department. The zip code 10026, with the lowest average immunization rate (47.6%) across all schools in these 15 zip codes, was not identified as a risky region by the NYC Health Department.

A closer look at which schools are located within these zip codes is available through the interactive table below. Users can review statistics on 40 at-risk schools in the 15 identified zip codes.

Summary

Based on the findings above, we recommend the New York City Department of Health follow a similar methodology when reviewing current and future policy.

Vaccination requirements isolated to certain zip codes ignores the very real possibility of the spread of measles on subways and public buses in a dense city like New York. Additionally, the geographically narrow application of such a policy runs the risk of marginalizing certain communities such as Orthodox Judaism.

A mandatory measles vaccination policy can better achieve target immunization rates by focusing on specific schools with low immunization coverage due to high rates of religious exemptions.

Furthermore, mandatory policy must not discriminate against students who are unable to obtain vaccines for medical reasons.