FROM SCIENCE TRANSLATIONAL MEDICINE

A new study links recent mumps outbreaks to the waning of the mumps vaccine – which researchers believe wears off in an average of 27 years – and not to heterologous virus genotypes.

“These observations indicate the need for either innovative clinical trial designs to measure the benefit of extending vaccine dosing schedules or new vaccines to address the problem of waning vaccine-induced protection,” the study authors wrote. The findings appeared in Science Translational Medicine .

The distribution of a mumps vaccine in the 1960s led to the near eradication of the disease with U.S. cases falling by more than 99%. However, large outbreaks have made the news over the last few years. There were more than 6,000 cases reported in the United States in 2016 and more than 5,000 in 2017, according to the Centers for Disease Control and Prevention, mainly on college campuses. (Physicians are not required to report mumps cases.)

The numbers over the past 2 years are the highest numbers by far since 2000, with the exception of 2006. The CDC attributes the 2016 and 2017 numbers to factors such as “the known effectiveness of the vaccine, waning immunity following vaccination, and the intensity of exposure to the virus in close-contact settings [such as a college campus] coupled with behaviors that increase the risk of transmission.”

This year, as of Feb. 24, the CDC stated that it has received reports of 304 cases in 32 states and Washington.

For the new study, Joseph A. Lewnard, PhD , and Yonatan H. Grad, MD, PhD , of the Harvard School of Public Health, Boston, examined six studies and estimated that mumps vaccinations provide protection for an average of 27 years (95% confidence interval, 16-51 years). They also reported finding no evidence that the effectiveness of vaccines was affected by new heterologous virus genotypes.

Their analysis also determined that outbreaks in the late 1980s and early 1990s (among teens), and from 2006 to present (in young adults), “aligned with peaks in mumps susceptibility of these age groups predicted to be due to loss of vaccine-derived protection.”

The authors suggested that third doses of vaccine or an improved mumps vaccine could provide added protection. “Although congregated U.S. military populations resemble high-risk groups based on their age distribution and close-contact environments, no outbreaks have been reported in the military since a policy of administering an MMR dose to incoming recruits, regardless of vaccination history, was adopted in 1991,” the researchers wrote, referring to a 2008 study ( Vaccine 2008, 26:494-501).

For now, however, “we expect population susceptibility to mumps to continue increasing as transient vaccine-derived immunity supersedes previous infection as the main determinant of mumps susceptibility in the U.S. population,” the authors wrote.

The study was funded by awards from the National Institute of General Medical Sciences and the Doris Duke Charitable Foundation. The study authors report grant funding (Pfizer) and consulting (Pfizer, GlaxoSmithKline) for work unrelated to the study.

fpnews@mdedge.com

SOURCE: Lenward JA et al. Sci Transl Med. 2018 Mar 21. doi: 10.1126/scitranslmed.aao5945 .

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