While undermining herd immunity in their communities, parents who decline measles vaccine for their children may be putting them and other kids at risk of a serious complication that is more common than once thought, researchers reported recently in New Orleans at IDWeek 2016.
A measles complication called subacute sclerosing panencephalitis (SSPE) may manifest years after the initial viral infection and appears to be uniformly fatal, the researchers reported. Long thought to be rare, SSPE incidence fell further off the radar with higher rates of routine measles vaccination. Measles vaccination is recommended at 1 year old, with a booster usually timed to occur at school entry. However, unvaccinated infants are at risk of acquiring measles and possibly SSPE.
The researchers looked at death certificates in California from 1998 to 2015 and found 17 cases of SPPE. SSPE is insidious, as the initial measles infection subsides, but the average age of the complication was 12 years. The age range of the SSPE cases was from 3 to 35, with patients typically displaying cognitive or ambulatory problems before the diagnosis was made, they reported.
Herd Immunity
The findings suggest that the complication may be much more common than previously thought, and certainly underscores the importance of vaccination in an era when false concerns about autism have undermined the uptake of the MMR vaccine. In that regard, herd immunity is critical, as infants too young for measles vaccination can get infected and later develop SSPE.
The condition may be dormant for years and was once thought to be as rare as only 1 in 100,000 cases following measles infection in young children. Subsequent research began suggesting the risk was much higher, and the findings presented at IDWeek indicate that SSPE could occur in about 1 in 600 children who acquire measles as infants before they can be vaccinated. Researchers do not know what triggers the virus to reactivate and cause SSPE.
Clinicians should be aware of the possibility of SSPE in patients with the aforementioned symptoms, even if found in older patients with no specific history of measles infection, the authors advised. Calling the findings “alarming,” co-author James D. Cherry, MD, MSc, professor of pediatrics and infectious diseases at the University of California Los Angeles, emphasized the importance of herd immunity in an IDWeek press conference.
“For measles vaccine, the first dose is about 95% [effective] and the other 5% remain susceptible,” Cherry said. “Right now, we don’t give the second dose of measles vaccine until school entry, roughly age 5. So, you have 1 in 20 children between the age of one and five that are susceptible. There is no reason you can’t give them the vaccine earlier. [Pediatric experts] say give the second dose if you are going to be traveling and things like that. What we have been talking about in California is going ahead and giving the second dose. So, you give the first dose at 12 months and then the second dose at 15 months. This is a gap in herd immunity that we could fix.”
The problem is that false fears of the vaccine have overridden the real dangers of measles infection, he observed.
“For parents who are not vaccinating their children because they are concerned about the risk of vaccines, we need to do an educational program,” Cherry said. “Where many people fall down on this is we start talking about risk of vaccines when we should be talking about risk of measles.”
The threshold to achieve measles herd immunity is estimated to be around a 90% vaccination rate, said Gary S. Marshall, MD, of the University of Louisville School of Medicine, Louisville, Ky.
“In other words, if you have a large community of a million people, and 90% of them are immune to measles, then theoretically an introduction of measles into that community shouldn’t propagate,” Marshall said. “However, non-immune people tend to geographically and spatially cluster. So, there may be 90% immunity in the community, but at [a particular] school it’s only 70%. Then a case is going to cause an outbreak. So, parents who are not vaccinating their children are really thinking very much of their own children, but not realizing that every unvaccinated child takes another chip away from the wall that prevents outbreaks of measles in the community.”
REFERENCE
- Wendorf K, Winter K, Harriman K, et al. Subacute Sclerosing Panencephalitis: The Devastating Measles Complication Is More Common Than We Think. Oral abstract session. IDWeek Oct. 26-30, 2016. New Orleans, LA.
