NEW YORK (Reuters Health) - An outbreak of mumps in the United States in 2006 -- the largest in two decades -- came at a time when the national two-dose vaccine coverage among adolescents was at an all-time high, public health officials reported in The New England Journal of Medicine.
According to Dr. Amy A. Parker, at the National Center for Immunization and Respiratory Diseases -- part of the Centers for Disease Control and Prevention in Atlanta -- and her associates, 6,584 cases of mumps were reported in 2006, and 75 percent of these cases occurred between March and May.
The mumps rate that year was 2.2 cases per 100,000 persons, compared with 1 case per 1,000,000 during the previous 5 years.
Eighty-five percent of cases occurred in eight contiguous midwestern states. The incidence was highest among young adults between 18 and 24 years old, nearly four times higher than for all of the other age groups combined. In the young adult group, 83 percent were attending college and 84 percent had received two doses of mumps vaccine.
The complication rate was 5 percent and hospitalization was necessary for 2 percent. Ten percent of males over the age of 12 developed orchitis -- inflammation of the testes -- and 2 percent of females over the age of 12 developed oophoritis or mastitis - inflammation of the ovaries or breast tissue, respectively.
About one third of males with orchitis will develop testicular atrophy. Infertility or high risk of pregnancy loss is associated with orchitis and females with mastitis may develop an abscess.
Less than 1 percent of the mumps cases progressed to meningitis, encephalitis, transient deafness or pancreatitis. One case of encephalitis resulted in long-term unresolved side effects as a result of the infection.
Waning immunity may have been a contributing factor, Parker's group suggests. Still, "attack rates in the most highly affected colleges in the 2006 outbreak were less than 6 percent, considerably lower than attack rates in both the prevaccine and one-dose-vaccine eras," they report. "Thus, mumps vaccine probably prevented United States patients from numbering in the tens or hundreds of thousands."
Future changes to national vaccine policy to provide higher or more durable immunity may involve administration of the second dose of the MMR (measles, mumps, rubella) vaccine at an older age, the authors suggest, or adding a third dose to the standard regimen.
SOURCE: The New England Journal of Medicine, April 10, 2008
