Increased reports of mumps in vaccinated populations prompted a review of the performance of mumps vaccines.
There was evidence of waning immunity, which is a likely factor in mumps outbreaks…
[O]utbreaks could not be prevented, despite high vaccination coverage with 2 doses of the Jeryl Lynn* vaccine strain.
[T]he recent resurgence of mumps in the United States, where outbreaks have occurred in the context of high 2-dose vaccination coverage, raised the question of whether available mumps vaccines are sufficiently effective to prevent outbreaks and achieve disease elimination.
13 outbreaks occurred among populations vaccinated only with the Jeryl Lynn strain…
[S]tudies included outbreaks in the United States (11 outbreaks), Canada (5), Europe (29, occurring in the United Kingdom, Switzerland, Italy, Spain, Austria, Belgium, Sweden, Ireland, Czech Republic, and Moldova), and Asia (5, occurring in Singapore, Korea, and Japan).
Articles reporting 27 of the 50 outbreaks contained information on populations vaccinated with 2 doses; of these 27 outbreaks, 10 involved the Jeryl Lynn vaccine strain…
[I]n an outbreak in Kansas… vaccination coverage in schools in the county where the outbreak occurred was 99.8%.
[T]he proportion of cases among vaccinated patients tended to increase with higher vaccination coverage rates.
[I]n 1 investigation of this outbreak at a large university in Kansas, the percentage of cases among patients vaccinated with 2 doses was 99.3%…
Although some studies did not find an association between time since vaccination and increased risk of disease, other studies conducted in the United States found persons vaccinated >5 years before the outbreak to be at higher risk of developing disease than persons vaccinated [less than or equal to] 5 years before the outbreak, suggestive of waning immunity.
The extent to which primary vaccine failure (i.e., no sero-conversion after vaccination) may contribute to mumps outbreaks was assessed through a review of 30 different studies of neutralizing antibody responses in initially seronegative children after vaccination with the Jeryl Lynn, RIT-4385, Urabe, or L-Zagreb mumps virus strains.
[R]ates of primary vaccine failure did not significantly differ for the Jeryl Lynn, RIT-4385, Urabe, and L-Zagreb vaccine strains, ranging from 5.4% to 8.8%.
[M]umps outbreaks have… occurred among populations with high 2-dose coverage.
For example, in 2006, a series of mumps outbreaks occurred in the United States, despite 2-dose vaccination coverage >95%, and in some investigations, >99% of patients had been vaccinated with 2 doses of vaccine.
Interestingly, the vaccine strain involved in those outbreaks, Jeryl Lynn, had been responsible for the near elimination of mumps in the United States until that time.
[T]here are numerous studies documenting decreases in antimumps virus antibody levels with time since vaccination and, in some cases, complete loss of seropositivity, even in recipients of 2 doses of vaccine.
During the mumps resurgence in the United States in 2006, most cases occurred in cohorts in which the most recent vaccination (second dose) was likely to have been administered [greater than or equal to] 10 years earlier. Of note, attack rates are not expected to continue to increase in older cohorts, because older individuals are likely to have been repeatedly exposed to wild-type mumps viruses earlier in life [and are therefore likely to have robust, natural, lifelong immunity]…
That outbreaks have recently occurred in populations with >95% 2-dose vaccine coverage strongly suggests that long-term prevention of mumps outbreaks with use of current vaccines and vaccination schedules may not be feasible.