Waning immunity may not have been only cause of 2006 mumps outbreak

Issue: November 2008

Although waning immunity may have played a key role in the 2006 U.S. mumps outbreak, this alone does not describe the epidemiological patterns observed, according to researchers from Atlanta.

“During the 2006 outbreak, many genetically identical isolates of genotype G were detected across the nation, accounting for 85% of cases. This suggests sustained transmission of a single viral lineage,” Albert E. Barskey, MPH, of the CDC, said during his presentation.

Barskey and colleagues compared epidemiologic data from the National Notifiable Disease Surveillance System on reported mumps cases during the pre-outbreak period (1994 to 2005), the 2006 outbreak and one year following the outbreak.

Data indicated the proportion of people who received two or more doses of the MMR vaccine increased from 37% before the outbreak to 57% during the 2006 outbreak. The proportion decreased to 53% in 2007.

The average age of patients with mumps fluctuated from age 11 years during 1994 to 2005, to age 22 years in 2006; it then decreased to age 18 years during 2007. According to the researchers, the increase in age of cases during the outbreak period supports the suggestion that waning immunity had an effect on the outbreak; however the decrease in age during 2007 does not.

Presented at: ICAAC/IDSA joint meeting. Oct. 25-28, 2008. Washington, DC.