Mumps immunity falls below optimal level

A regional mumps resurgence and a lower national immunity in the U.S. mean physicians may be seeing more mumps cases in their sick patients, according to the authors of a new study.

A study published online July 27 in The Journal of Infectious Diseases found that Americans' seroprevalence of antibody to mumps between 1999 and 2004 was below the estimated level of immunity needed to eliminate the illness in the U.S.

The findings come as a resurgence of the virus started in June 2009 and continues to spread largely through Orthodox Jewish communities in New York and New Jersey. More than 1,500 cases have been reported, according to the Centers for Disease Control and Prevention.

The largest mumps outbreak in the U.S. in 20 years occurred in 2006, with 6,584 cases reported, mostly in Midwest states, according to the study. In both outbreaks, a majority of those infected received at least one of the two recommended doses of mumps vaccine.

"Doctors should understand that mumps can still occur [in the U.S.]. If we want to improve population immunity, we should ensure children are appropriately" vaccinated against the disease, said Preeta K. Kutty, MD, MPH, the primary study author and a medical epidemiologist for the CDC.

Cases of the disease should be reported promptly to state health departments, and infected patients should limit interaction with others.

Researchers examined data on 15,383 people age 6 to 49 who participated in the National Health and Nutrition Examination Survey between 1999 and 2004. They tested participants' serum for the presence of immunoglobulin G antibody to the mumps virus as a measure of the population's immunity against the disease.

The study found that about 90% of participants had antibody to the mumps virus (link). That figure falls just below the estimated level of immunity (92%) needed to prevent community transmission and outbreaks of the virus, Dr. Kutty said.

Participants born between 1977 and 1998 -- the group with the highest disease incidence during the 2006 outbreak -- had a seroprevalence of about 90%. Among white people, who were more affected than other races during the outbreak, 87.8% had antibodies to mumps.

Participants who were born outside the U.S. had a higher level of seroprevalence (94.7%) than people who were born in the U.S. (89%). Study authors said the finding could reflect a greater circulation of the virus, and thus more exposure to the disease, in foreign countries.

The CDC recommends that physicians administer one dose of the measles, mumps and rubella vaccine and one dose of the varicella immunization to children 12 to 47 months. Doctors can use the combined measles, mumps, rubella and varicella vaccine to administer the recommended second dose between 15 months and 12 years.

The MMR vaccine should be given to adults 19 to 53 who lack documentation of vaccination or have no evidence of prior infection. Adults born before 1957 generally are considered immune to measles and mumps. But unvaccinated health professionals born before 1957 should receive two doses of MMR.

Researchers are examining whether a third mumps dose is needed to ensure immunity against the virus, said William J. Bellini, PhD, senior study author and chief of the CDC's Measles, Mumps, Rubella and Herpesvirus Laboratory Branch.