As Millions dodge Measles Vaccine, Nation's Herd Immunity nears Tipping Point

October 15th, 2015

Clinicians should be vigilant for incoming measles cases, as some 9 million U.S. children — 1 in 8 of those age 17 and younger — are now susceptible to a virus that can cause chaotic outbreaks in healthcare facilities, researchers recently reported in San Diego at IDWeek 2015.

If the trend continues to increase, millions of susceptible youth — and eventually young adults — could reach a tipping point in population herd immunity, meaning more frequent and sustained measles outbreaks could occur.

“We can’t be complacent — we don’t have a very wide buffer before these population-level immunity estimates start dipping below critical levels,” said lead researcher Robert Bednarczyk, PhD, a professor in the Rollins School of Public Health at Emory University in Atlanta. “If our measles immunization starts to falter we could see immunity below what we need to [prevent] transmission. We could start seeing larger outbreaks or outbreaks that sustain over longer periods of time.”

An undiagnosed case of measles in a hospital can set off a frantic investigation to determine exposures and ensure immune status among staff and patients. Though willful susceptibility endangers high risk groups like the immune compromised and infants not yet indicated for vaccination, an anti-vaccine movement in the U.S. has cast suspicion on all immunizations and linked the measles MMR shot erroneously with autism. As a result a disease once declared eliminated in the United States threatens to regain a foothold as children denied vaccination by their parents now become susceptible young adults.

“There is a creeping nature to the problem in the sense that vaccine hesitancy is really coming of age to some degree,” said Matthew Zahn, MD, of the Orange County (CA) Health Care Agency. “We now see kids of 15 or 18 years of age whose parents have not vaccinated them because they have concerns about the safety of the vaccines.”

Even if current immunization rates don’t further decline, there are pockets and clusters of vulnerable populations who can set off rapidly expanding measles outbreaks. Participating in an IDWeek measles press conference, Zahn said his county had 35 cases of measles at the beginning of this year as part of a large national outbreak that began at Disneyland.

“It was sobering to recognize that one exposure can cause so many cases around the country,” he said “As a pediatrician and a public health officer it is frustrating to admit children to hospitals for a disease that is very preventable and generally we felt was gone.”

For more on this story see the November 2015 issue of Hospital Infection Control & Prevention.