Large Mumps Outbreak Characterized by 2-Dose Vaccine Failure
Authors and Disclosures
Laurie Barclay, MD
Disclosure: Laurie Barclay, MD, has disclosed no relevant financial relationships.
Désirée Lie, MD, MSEd, has disclosed no relevant financial relationships.
Brande Nicole Martin Disclosure:no relevant financial information.
April 9, 2008 — Despite a high coverage rate with 2 doses of mumps-containing vaccine, a large mumps outbreak occurred among midwestern college-age adults who probably received the second dose as schoolchildren, according to the results of a study reported in the April 10 issue of the New England Journal of Medicine. The study authors suggest that a more effective mumps vaccine or changes in vaccine policy may be warranted.
"The widespread use of a second dose of mumps vaccine among U.S. schoolchildren beginning in 1990 was followed by historically low reports of mumps cases," write Gustavo H. Dayan, MD, from the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, and colleagues. "A 2010 elimination goal was established, but in 2006 the largest mumps outbreak in two decades occurred in the United States."
The investigators reviewed data on mumps cases reported in the United States during 2006, detailed case data from the states that were most highly affected, and vaccination-coverage data obtained in 3 nationwide surveys.
Of 6584 cases of mumps reported in 2006, a total of 76% occurred between March and May, and 85% of patients lived in 8 contiguous midwestern states. Although 85 patients were hospitalized, there were no deaths.
The national incidence of mumps was 2.2 per 100,000. The highest incidence was in persons 18 to 24 years of age, with an incidence 3.7 times that of all other age groups combined; subgroup analysis revealed that 83% of these patients were currently enrolled in college.
Of the patients in 8 highly affected states who had known vaccination status, 63% overall and 84% of those aged 18 to 24 years had received 2 doses of mumps vaccine. National coverage of 1-dose mumps vaccination among preschoolers was 89% or more nationwide and 86% or more in highly affected states during the 12 years preceding the outbreak. In 2006, the national 2-dose coverage was 87% among adolescents, the highest rate in US history.
"Despite a high coverage rate with two doses of mumps-containing vaccine, a large mumps outbreak occurred, characterized by two-dose vaccine failure, particularly among midwestern college-age adults who probably received the second dose as schoolchildren," the study authors write. "A more effective mumps vaccine or changes in vaccine policy may be needed to avert future outbreaks and achieve the elimination of mumps."
Possible explanations for the outbreak may include waning immunity secondary to a lack of natural exposure, or mumps vaccine–induced immunity (derived from genotype A virus) may be less effective against heterologous strains (eg, G genotype).
Limitations of the study include cases of mumps reported through a passive surveillance system with unknown sensitivity; inability to assess vaccine effectiveness with the use of outbreak surveillance data because of high vaccine coverage among patients with mumps; and the ability of laboratory testing to confirm, but not to rule out, mumps.
"Future studies will help to evaluate national vaccine policy, including whether the administration of a second dose of MMR [measles-mumps-rubella] vaccine at a later age or the administration of a third dose would provide higher or more durable immunity," the study authors conclude.
Dr. Dayan, who was employed at the CDC during the preparation of this article, has disclosed being employed at Sanofi Pasteur. Dr. O'Keefe holds an equity interest in Abbott Laboratories, and Ms. Kenyon has received a federal Emerging Infections and Protection grant. The other study authors have disclosed no relevant financial relationships.
N Engl J Med. 2008;358:1580-1589.
Reports of mumps infection dropped dramatically after the implementation of a policy of 1-dose mumps immunization in 1977 in the United States. In the 1980s, outbreaks of mumps occurred in vaccinated and unvaccinated adolescents and young adults, but since the requirement for 2-dose MMR vaccination, the rates of mumps had decreased with a goal of 2010 for elimination of mumps in the United States.
However, in 2006, the United States experienced the largest mumps epidemic in 2 decades, primarily in 8 midwestern states and in young adults aged 18 to 24 years. The epidemic was unexpected, abrupt, and focal. This study describes patterns associated with the outbreak and vaccination histories of those affected by the epidemic.
Mumps cases were classified though the National Notifiable Diseases Surveillance System from state health departments to the CDC.
A confirmed case was one that met clinical and laboratory criteria, whereas a probable case met only clinical criteria.
3 times were defined: preresurgence (2000-2005), resurgence (2006), and postresurgence (January - June 2007).
Case data from the 8 most severely affected midwestern states included vaccination status, self-reported ethnicity, and college attendance for 4 states.
Data on mumps vaccination rates were obtained from 4 sources: the US Immunization Survey, the National Immunization Survey, the National Health Interview Survey, and school vaccination surveys.
After 1967, reported mumps cases decreased by 98%, with increased numbers in the 1980s followed by low case counts from 2000 to 2005 when less than 350 cases were reported annually.
In January 2006, mumps cases were noted on college campuses, with a peak occurring in April 2006 and 40 US states reporting 2786 cases.
By December 31, 2006, a total of 6584 cases and 85 hospitalizations for mumps had been reported, with no deaths.
No large outbreaks occurred in primary or secondary schools.
In the postresurgence period, the case rate was 60 per month with a total of 359 cases for 6 months.
In the preresurgence period, the incidence of mumps was less than 1 case per million.
During the 2006 resurgence, the national incidence was 2.2 per 100,000 persons, and 8 states had the highest case counts (range, 170 - 1964) and incidence rates (2.9 - 65.9 per 100,000 persons).
These 8 states accounted for 85% of cases and comprised only 13% of the US population.
Mumps was confirmed by polymerase-chain–reaction assay or viral isolation in all highly affected US states.
The rate of 1-dose vaccination was 78% to 80% among 24-month-old children in the 1980s.
From 1995 to 2006, 1-dose coverage for children aged 19 to 35 months was 90% to 93% and 86% to 96% in the 8 highly affected US states.
From 1997 to 2003, 2-dose mumps vaccine coverage among adolescents aged 13 to 15 years increased from 68% to 77%.
In 2006, 2-dose vaccine coverage between 13 and 17 years was 87%.
In the period from 2006 to 2007, second-dose coverage for kindergartners and first-graders was 81% to 100% (mean coverage, 97%).
In the 8 highly affected US states, 29% of infected persons were aged 18 to 24 years; among those with known vaccination status, 13% had received no vaccine, 25% had received 1 dose, and 63% had received 2 or more doses.
Less than 4% of those younger than 30 years were unvaccinated.
Among those 30 years or older, the proportion of unvaccinated persons increased progressively to 73%.
64% of those infected were women, and whites had an incidence rate twice as high as that of other races or ethnic groups.
Incidence of infection was highest among college students aged 18 to 24 years and recipients of 2 doses of mumps vaccine.
The authors suggested that vaccine failure, waning immunity, high population density, incomplete immunity to wild virus, genotype G virus, and infection imported from another region in the world contributed to the outbreak.
The authors advocated evaluation of national policy on vaccination for mumps including consideration of administration of a third dose to provide higher or more durable immunity.
Pearls for Practice
In the mumps resurgence of 2006, a total of 8 US states representing 13% of the national population were most affected, with 85% of cases.
In the highly affected US states, those who were college students ages 18 to 24 years old, women, white, and those who received a 2-dose schedule of vaccination were most likely to be infected during the 2006 mumps outbreak.
Wednesday, April 16, 2008
Mumps Outbreak may indicate another vaccine failure.
It seems as if this story is just another indicator that the vaccine propaganda is really a failed initiative.