Resurgence of Measles, Pertussis Fueled by Vaccine Refusals

Posted on March 22, 2016 by Dr. Francis Collins

Credit: Centers for Disease Control and Prevention

I was born in 1950 and was home-schooled until the 6th grade. Thus, I missed exposure to several childhood illnesses that affected most of my generation. I never gave it much thought until, as a medical resident in North Carolina in 1979, I came down with a potentially life-threatening febrile illness that required hospitalization. Only after four days of 105 degree fever did a rash appear, and the diagnosis was made: measles. That was the sickest I have ever been. It turned out that one of my daughter’s school friends had developed measles in a small outbreak of unvaccinated kids in Chapel Hill, and I had been exposed to her. I was born too early to have been vaccinated.

But for most people born in the United States after the 1960s, they have never had to experience the high fever and rash of the measles or the coughing fits of pertussis, commonly known as whooping cough. That’s because these extremely contagious and potentially life-threatening diseases have been controlled with the use of highly effective vaccines and strong vaccination programs. And yet, the number of Americans sickened with measles and pertussis each year has recently crept back up.

Now, an NIH-funded report confirms that many of the recent outbreaks of these vaccine-preventable diseases have been fueled by refusal by some parents to have their children vaccinated [1]. The findings, published recently in JAMA, come as an important reminder that successful eradication of infectious diseases depends not only on the availability of safe and effective vaccines, but also on effective communication about the vaccines and the diseases they prevent.

In the study, led by Saad Omer of Emory University, Atlanta, researchers searched the medical literature for all reports of measles outbreaks in the United States from January 2000 through November 2015. They did a similar search for pertussis outbreaks since 1977, when cases of this disease reached their lowest point in the U.S.

Omer and his colleagues identified 18 published reports of measles outbreaks, describing more than 1,400 cases in people who ranged in age from 2 weeks to 84 years old. Although vaccination information was lacking for about 29 percent of the people, 804 cases (56.8 percent) were confirmed to be unvaccinated. Only 199 cases (14 percent) involved individuals known to have received a measles-containing vaccine.

The researchers next drilled down to seven studies with the most-detailed vaccination summaries to look for those who were intentionally unvaccinated. They found 574 out of 970 individuals were unvaccinated, despite being old enough to receive the measles-mumps-rubella (MMR) vaccine. Of the 574 people, 405 had filed an exemption for religious or philosophical reasons.

Omer and his colleagues also identified 32 reported pertussis outbreaks, totaling more than 10,000 cases in people whose vaccination status was known. In the five largest statewide epidemics, the data show that a substantial number—at least 1 in 4—of those who became ill were unvaccinated.

Unlike the measles vaccine, the pertussis vaccine can lose some of its effectiveness over time. As a result, some pertussis outbreaks have arisen in places with high vaccination rates. Still, the evidence shows that people who are intentionally unvaccinated have played an important role in many of the recent pertussis outbreaks.

The researchers also noted that the contribution of vaccine refusal to outbreaks of both measles and pertussis often appears greatest early in an epidemic. This trend suggests that vaccine refusers provide “pockets of susceptibility” that can help to trigger an outbreak.

This is an especially important point. Parents have a responsibility not only to their own children, but to their communities—it’s only by achieving a very high level of population immunity that outbreaks can be prevented. Vaccination is particularly crucial for children with cancer and other diseases that cause immunosuppression. They cannot be vaccinated safely, but are at high risk of severe consequences if they are infected—and, thus, they depend on the community’s so-called “herd immunity” for protection against a potentially fatal illness.

While some parents continue to express concern about a possible link between vaccines and autism spectrum disorders, the original report claiming this connection has been debunked and retracted. A large number of carefully designed follow up studies have been carried out, and the overwhelming weight of scientific evidence shows no evidence for such a link. That’s why it continues to be so important to get the word out to parents: Have your kids vaccinated. The Centers for Disease Control and Prevention (CDC) recommends that all children receive a first dose of the MMR vaccine by 12 to 15 months of age, and a second dose between 4 to 6 years old. [2]. For pertussis, CDC recommends that children receive four doses of the diphtheria, tetanus and pertussis vaccines (DTaP) in the first 1½ years of life and a final dose between 4 and 6 years old [3].

References:

[1] Association Between Vaccine Refusal and Vaccine-Preventable Diseases in the United States: A Review of Measles and Pertussis. Phadke VK, Bednarczyk RA, Salmon DA, Omer SB. JAMA. 2016 Mar 15;315(11):1149-1158.

[2] Measles (Rubeola), Centers for Disease Control and Prevention, July 1, 2015.

[3] Pertussis (Whooping Cough) Vaccination, Centers for Disease Control and Prevention, February 3, 2016.

Links:

Vaccines (National Institute of Allergy and Infectious Diseases/NIAID)

Community Immunity (Vaccines.gov)

Measles (MedlinePlus Medical Encyclopedia)

Pertussis (Whooping Cough) (Centers for Disease Control and Prevention)

Saad Omer (Emory University, Atlanta, GA)

NIH Support: National Institute of Allergy and Infectious Diseases