The current measles outbreak in the United States has now touched 17 states and the District of Columbia, the U.S. Centers for Disease Control and Prevention announced February 9. So far, 121 cases of measles have been reported nationwide in 2015, up from a total of 102 cases a week earlier, CDC data show. The unusual appearance of measles has some researchers pondering limits on avenues for vaccine avoidance and the possibility of earlier vaccination for babies.
The numbers may appear low, but the threat is high, says William Schaffner, an infectious disease physician at Vanderbilt University in Nashville. “I’m worried about measles reestablishing itself,” he says. Because of its high infectivity, measles needs only a few unprotected people to gain a foothold in a subpopulation, such as a school or church.
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The current outbreak exemplifies what can happen when herd immunity is weakened. Herd immunity is the protection conferred on an entire community, or “herd,” when a large fraction of its residents are immunized against a particular disease. But herd immunity can falter, as it has with whooping cough. Vaccine refusals and delays — coupled with a switch to a weaker vaccine — have allowed pertussis to stage a comeback in the United States after it was nearly wiped out (SN: 4/19/14, p. 22).
Herd immunity against measles peaked around 15 years ago in the United States. Thanks to widespread immunization, annual cases were fewer than 50 a year, says pediatrician Samuel Katz of Duke University, a coinventor of the measles vaccine. At that point, he and other doctors expected to see the occasional case show up from abroad. But, he says, “we couldn’t have anticipated this. Not at all.”
From 2001 to 2010, the median number of cases was about 60 a year, Anne Schuchat, director of CDC’s National Center for Immunization and Respiratory Diseases, said at a recent briefing. But in 2014, the United States recorded 644 cases scattered across 27 states, CDC data show. CDC and California Health Department officials say that the vast majority of these are showing up in unvaccinated or partially vaccinated individuals, or in people for whom vaccination history or previous exposure is unknown. Delaying initial vaccination also leaves a baby at risk longer, Schuchat noted.
The course of the 2015 outbreak remains unclear so far. In the latest count, several states report a single case. California has 88, with most stemming from an outbreak at Disneyland that spawned infections in December and is apparently the origin of most of the cases nationwide.
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Measles can cause very high fever spikes and complications such as brain damage and deafness. Older people are largely protected because nearly all had a brush with measles in childhood and retain immunity to it. Measles vaccination —part of the MMR shot that also covers mumps and rubella —is preventive, but it is not recommended for infants until they are at least 12 months of age. Residual antibodies from the mother limit the shot’s effectiveness until that age, Schaffner says. It’s likely that a mom’s residual protection against the disease lasts through 6 months of age. But after that, he says, “it’s a gray area.”
It’s reasonable to assume that a baby 6 months to 12 months old could generate some protection from a measles shot, Katz says, and some studies have shown as much. The key would be to make sure such a child later gets the regular two-shot regimen to establish full protection, he says. He expects the CDC and pediatricians to consider shifting the official recommendation to this earlier vaccination schedule.
In people sick with measles, drugs can reduce fever but there is no cure. An experimental drug is still in the animal-testing stage (SN: 5/17/14, p. 10).
Schaffner says there could be an upside to the current outbreak — it has increased scrutiny of vaccine avoidance. “It’s brought forth a concept I haven’t seen discussed publicly, that you are vaccinating not just yourself but the community, and that you have community obligations.”
The other potential benefit, Katz says, it that the measles outbreak might induce states to limit the philosophical exemption against vaccines that allows parents to enroll unvaccinated children in school. He supports efforts at the state level to require parents seeking such exemptions to get physician approval first.