By: Katherine Lewis

Editor’s Note: This article is the second of a 3-part series on measles and vaccines.

Although the US has significantly greater vaccine coverage than Madagascar, 6 outbreaks (defined as 3 or more cases) have been reported so far this year in New York, Washington, Texas, Illinois, and California due to gaps in vaccine coverage. Cases have also been reported in Colorado, Connecticut, Georgia, Kentucky, New Hampshire, New Jersey, and Oregon. The Centers for Disease Control and Prevention (CDC) confirmed 228 individual cases of measles were in the US between January 1st and March 7th, 2019. According to the CDC, these outbreaks are “linked to travelers who brought measles back from other countries such as Israel and Ukraine, where large measles outbreaks are occurring.”

Graph showing that the number of measles cases in the US decreased drastically between 1950 and 1985.
Image by the Centers for Disease Control and Prevention. Measles was declared eliminated in the US in 2000 following the widespread success of the measles vaccine program.

Once measles arrives in the US, it spreads easily if it comes into contact with individuals who are not vaccinated or communities who have low rates of vaccination. For example, the 2018 outbreaks in New York State, New York City, and New Jersey were linked to travelers bringing the disease back with them from Israel, where it spread rapidly among unvaccinated individuals in Orthodox Jewish communities. The CDC provides travel notices for measles on their website and recommends that all individuals 12 months or older receive two doses of the MMR vaccine prior to international travel (it is also recommended that infants 6-11 months receive one dose). Despite a high national rate of vaccine coverage, communities in which the coverage is significantly below the national average represent pockets of susceptibility, which increases the risk for those living there. For example, an outbreak of 383 cases in 2014 most severely impacted Amish communities in Ohio, where vaccine coverage was poor. 

It is crucial that the US work to close the gap between existing coverage rates and the threshold for herd immunity (which the point at which a sufficient proportion of a community is protected to prevent the spread of a contagious disease, for measles this is 95% coverage) as well as the gap between individual communities and the national average. These strategies are crucial to prevent the unnecessary spread of measles and avoid widespread outbreaks like those in Madagascar.

Infographic depicting how herd immunity functions in a population. When a large portion of the population is immune, the spread of the disease decreases.
Image by the National Institute of Allergy and Infectious Diseases.

According to a report published by the CDC, “the percentage of children [in the US] who have received no vaccines has increased, reaching 1.3% for children born in 2015, compared with 0.3% among those 19-35 months when surveyed in 2001.” The report found that unvaccinated children are significantly more likely to be uninsured than vaccinated children (17.2% compared to the national rate of 2.8%), pointing to flaws in the Vaccines for Children (VFC) program, which provides free vaccines to program participants.

Despite a high national rate of vaccine coverage, communities in which the coverage is significantly below the national average represent pockets of susceptibility, which increases the risk for those living there.

Additionally, the report noted the role of parental decisions in whether or not their child is vaccinated. This issue has gained media attention recently with the prevalence of anti-vaccine campaigns, wherein parents refuse to vaccinate their children based on fears concerning the safety of vaccine use. This concern has sparked national debate over the respective powers of the government and of the child’s parents in determining whether or not the child receives vaccinations.

Next in the series, we will cover the recent Senate committee hearing on vaccine use in the US.

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