Study: Small drop in vaccine uptake can trigger measles outbreak

A modeling study today in JAMA Pediatrics shows that even a 5% reduction in vaccine coverage could trigger a significant measles outbreak.

"It doesn’t take much to ignite a measles epidemic," said Peter J. Hotez, MD, PhD, in an interview. Hotez is the Dean of the National School of Tropical Medicine at Baylor College of Medicine and a study author. "When you have a virus with a high reproductive number, you can see an outbreak as soon as vaccine coverage drops."

Ninety percent of unvaccinated people exposed to measles will contract the virus, which can cause mild to severe illness and even death. Measles, like mumps and diphtheria, has a high "R" or reproductive value; meaning it is transmitted easily and quickly in naive populations.

The best defense against viruses with high R values is vaccine coverage targeting 90% to 95% of the population, but Hotez said recent waves of vaccine hesitancy have created enough dips in some communities' vaccine coverage to allow outbreaks.

Hotez said the modeling study was conceived after the April measles outbreak in Minneapolis. The outbreak took hold in the Somali-American population of the city, which has displayed vaccine hesitancy because of unfounded fears the the measles, mumps, and rubella (MMR) vaccine causes autism. To date, there have been 79 cases of measles diagnosed in Minnesota.

"As we've seen in Minnesota, measles is not a benign disease," said Hotez. "People get hospitalized."

5% drop in coverage could cost $2.1 million

To conduct the study, Hotez and colleague Nathan Lo used data from the US Centers for Disease Control and Prevention to simulate county-level MMR vaccination coverage among children ages 2 to 11. A 5% reduction in coverage led to a tripling of measles cases.

That threefold increase does not take into account unvaccinated infants and older adults who may contract the disease during an outbreak. Hotez estimates that each measles case costs $20,000 in public sector costs, which means a tripling of cases could cost US taxpayers more than $2.1 million annually.

"Our emphasis here is on the 18 states in this country that still allow for non-medical vaccine exemptions," said Hotez. "We have to end those exemptions and close the loopholes to prevent these preventable outbreaks."

See also:

Jul 24 JAMA Pediatrics study 

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