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Small drops in measles vaccination have disproportionate effects, new study finds

Measles is ridiculously contagious: Sneezed from someone’s nose, the virus lingers in the air, able to infect others who enter the same room hours later. It spreads far more easily than HIV, Ebola or Zika. Before an effective vaccine was introduced in 1963, measles killed 2 million children worldwide each year.

Thanks to the vaccine, we now have tenuous control over measles, with the tantalizing possibility of eliminating it entirely. But progress toward that goal could easily backslide. Although vaccination ended continuous person-to-person transmission of measles in the United States in 2000, travelers visiting other regions of the world still bring back cases that can cause outbreaks in unvaccinated people. And each year, several states consider whether to relax their vaccination laws by expanding personal-belief exemptions to vaccination.

But losing our grip on the disease would be costly, as a new paper published today in JAMA Pediatrics describes. The study, from Stanford and Baylor College of Medicine, found that small declines in U.S. childhood vaccination rates would cause disproportionately large increases in the number of U.S. measles cases and the public-health costs of the disease. Our press release explains:

Among children ages 2 to 11, a five percent drop in use of the measles, mumps and rubella (MMR) vaccine would triple the number of annual measles cases in this age group, the study found. These additional measles cases would increase annual public health expenditures by at least $2.1 million.

If kids younger than 2 are added to the estimate, the public-health cost goes up by at least another $400,000 per year. The cost per case of measles is at least $20,000.

Stanford MD/PhD student Nathan Lo, the study’s first author, noted that although national vaccination rates are high overall, geographic clusters of unvaccinated people are very susceptible to outbreaks — and state vaccination policies play into whether such clusters can form. California eliminated its personal-belief exemption in 2015 after a large measles outbreak originated in Disneyland, but some states are going the opposite direction:

Lo hopes state lawmakers will consider the study’s findings as they contemplate vaccination policies, especially non-medical personal belief exemptions to childhood vaccination requirements. “Every year, an increasing number of states are debating non-medical exemptions, which are a critical driver of vaccination coverage,” he said. “This study quantifies the consequences of rise in measles cases and state dollars that will be spent if personal belief exemptions that can reduce vaccine coverage are in place."

While writing about the research, I also chatted with Stanford infectious disease expert Yvonne Maldonado, MD, who was not involved in the work.

“Measles is one of the few diseases we could eliminate,” Maldonado told me. Compared to many other contagious diseases, measles has simple biology: It affects only humans and doesn’t linger in the body. To keep existing, the disease must keep jumping from person to person. Vaccination is a powerful way to interrupt that, and the measles vaccine has been shown for decades to be safe and effective.

The extreme contagiousness of measles adds a wrinkle to vaccination efforts, though. When smallpox was close to eradication in the 1970s, public health officials used “ring vaccination,” sending teams of health workers to vaccinate everyone who had been in contact with each new patient. Because smallpox spreads fairly slowly, this worked.

“Measles is so highly infectious, you can’t do ring vaccination,” Maldonado said. “By the time you get to a case, it is already spreading through the population. We really need to make sure all children are vaccinated with two doses of vaccine.”

Previously: Infectious disease expert discusses concerns about undervaccination and California's measles outbreak, Measles is disappearing from the Western hemisphere and A look at the causes and potential cost of the U.S. measles outbreaks
Electron micrograph of measles virus by Sanofi Pasteur

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