The number of measles cases has skyrocketed to 626 as of April 19 and is almost certain to set a record in 2019 for the most infections since the Centers for Disease Control and Prevention declared the virus eliminated in 2000.
The outbreak of measles this year reflects a major increase in recent years of parents refusing to vaccinate their kids and taking advantage of new state laws that have permitted exemptions to vaccine mandates.
Before the measles vaccine was developed in 1963, an estimated 3 million to 4 million children were infected each year, often before the age of 15. The trend would have continued if it were not for John F. Enders, now known as the father of modern vaccines, and Thomas C. Peebles. Both researchers spent over a decade studying the virus and isolated it from the blood of an infected Boston teenager. They transformed the virus into the country’s first measles vaccine. It was then improved and widely distributed in 1968, and the U.S. has been using it ever since.
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The number of measles cases plummeted by 1981 but rose again just eight years later. Infectious disease doctors decided a second vaccine in school children would offer better protection. With that second vaccine, the virus was eliminated by 2000.
There is a distinction between “eliminated” and “eradicated.” In saying that measles was eliminated, the CDC does not mean the virus would never reemerge in the future. Rather, it means the virus was no longer an epidemic in the U.S. To say a disease is eradicated is to say that it no longer poses a threat to the global host population.
The breakthrough vaccine did not make its way overseas. Large outbreaks, beginning in 2006, have been traced to patients who had traveled abroad and returned from European countries, India, Israel, and other places. Measles is pervasive in other countries, with about 20 million cases worldwide. Still, the annual number of cases across the U.S. never exceeded 220 between 2001 and 2013, hardly comparable to outbreaks prior to the 1960s.
In 2014, the virus returned in earnest, climbing to 644 cases from almost 24 different nationwide outbreaks. Forty-two confirmed cases were traced back to Disneyland, according to California public health officials. The cause, they say, was unvaccinated travelers from overseas who gravitate toward tourist attractions and public parks. The outbreak continued well into 2015, but the CDC still considers it eliminated.
[Related: NYC declares health emergency amid measles outbreak]
Meanwhile, at some point between 2000 and now, the once-celebrated measles vaccine became highly controversial among segments of the population. Parents became increasingly skeptical that the vaccine was safe, choosing not to immunize their children. The reasons for the rise in skepticism are complex and not fully understood, but one major factor was the dissemination of a paper published in the Lancet in 1998 that tied the measles, mumps, and rubella, or MMR, vaccine to autism. The study was retracted in 2010, and other research has not indicated a link between vaccines and autism, yet the perception that vaccines cause autism has proved resilient.
Starting in the late 2000s, parents across the country became more outspoken about their opposition to vaccines. Celebrities including Jenny McCarthy, Alicia Silverstone, and Rob Schneider promoted skepticism about vaccine science, telling parents that the risks of vaccination for their kids outweigh the benefits. McCarthy, in particular, soon became the face of the “anti-vax” movement. The rise of social media, too, allowed anti-vaccination parents to easily share their views and win over others.
Many parents who choose not to vaccinate do so on moral grounds, because some vaccines were derived using aborted fetal tissue. During a rubella epidemic in the 1960s, Stanley Plotkin found that about 1% of women in a Philadelphia hospital elected to abort fetuses infected with rubella. Plotkin was able to isolate the rubella virus in an aborted fetus’ kidney. The cell lines that Plotkin used are still employed today, as the cells can be divided over and over again and still produce cells necessary for the vaccine. No more fetal cells are needed to carry on making these vaccines. Still, many conservative religious groups choose not to administer the MMR vaccine due to its origins in abortion.
Most states now permit philosophical and religious exemptions from vaccinations. All but three states, California, West Virginia, and Mississippi, allow parents to refuse otherwise mandatory vaccinations based on their religious beliefs.
The number of parents taking advantage of these exemptions is rising steadily. A 2018 CDC report found that the rate of unvaccinated kids born in 2011 had risen by about 18,000 in those born in 2015, making those kids increasingly vulnerable to contracting the virus. CDC researchers have also linked the rise in measles cases in the 2010s — albeit to extremely low levels by historical standards — to a failure to vaccinate.
Most recently, the number of measles cases in a small Brooklyn neighborhood with a high population of Orthodox Jewish families has reached 359 cases, prompting Mayor Bill de Blasio to declare it a public health emergency and make the measles vaccine mandatory for school-age children.
