An outbreak of mumps in 12 fully vaccinated students attending University of Florida, Gainesville campus had county health officials scratching their heads at the end of May. According to one media report, an Alachua County Health Department spokesperson said, “These things do happen. It’s a phenomenon that’s not completely understood,” and reassured students and the public that the MMR vaccine “is a safe vaccine, it’s an effective vaccine even though we have this outbreak in a group of vaccinated individuals.1
By June 4, WTSP News reported that the number of students on campus with mumps was up to 24 and a University of Florida spokesperson confirmed that all 24 students were vaccinated. Reportedly, a Florida Department of Health spokesperson said the majority of outbreaks in the U.S. are identified on college campuses and that most mumps cases go undiagnosed due to a lack of testing and reporting.2
2019: More Than 1,000 Mumps Cases Reported in U.S.
According to the CDC, “mumps outbreaks are not reportable” but there have been 1,002 cases of mumps infections reported in 42 states and the District of Columbia between Jan. 1 and May 24, 2019 in the U.S., with an increase of 266 reported cases since Apr. 26. The CDC.gov website states that, “mumps outbreaks can still occur in U.S. communities of people who previously had one or two doses of MMR vaccine.3 The CDC also states that, “a person with two doses of MMR vaccine has about an 88 percent reduction in risk for mumps.”4
The numbers of mumps infections reported in the U.S. this year exceeds the number of measles cases reported this year, which totaled 931 cases confirmed through May 31, 2019.5 According to one page on the CDC’s website, “mumps outbreaks are not reportable.”6 However, according to another page on the CDC’s website, mumps has been a reportable disease for many years.7
For more than a decade, there have been continuing reports published in the medical literature documenting mumps outbreaks in highly vaccinated populations. Most of the individuals who got mumps had received one or two doses of MMR vaccine, especially college students and young adults.8
Asymptomatic Mumps Infections
Both unvaccinated and vaccinated persons can be asymptomatically infected with mumps and transmit the infection without knowing it to other people. In 2015, the CDC stated, “Before the introduction of the mumps vaccine in the United States in 1967, 15% to 27% of infections were asymptomatic. In the post-vaccine era, it is difficult to estimate the number of asymptomatic infections, because it is unclear how vaccine modifies clinical presentation.”9
2008: Waning Immunity, Different Vaccine Strains & Mumps Outbreak Strains
In 2008, researchers from Sanofi Pasteur and the U.S. Food and Drug Administration (FDA) evaluated mumps outbreaks and mumps vaccine (MMR) effectiveness. After reviewing 47 published articles on mumps outbreaks in vaccinated populations, they reported that there is “evidence of waning immunity, which is likely a factor in mumps outbreaks, aggravated by possible antigenic differences between the vaccine strain and outbreak strains.” Although mumps vaccine was found to be protective, researchers said that, “vaccine effectiveness during outbreaks was lower than that reported during controlled clinical trials.”10
Specifically, they found that:
- In 2006, “a series of mumps outbreaks occurred in the United States, despite 2-dose vaccination coverage of over 95 percent, and in some investigations, over 99 percent of patients had been vaccinated with 2 doses of [MMR] vaccine;”
- “Viruses isolated from recent mumps outbreaks differed phylogenically and, possibly, antigenically from the vaccine viruses used;” The Jeryl Lynn RIT-4384 mumps vaccine strains in MMR are genotype A viruses, while wild-type viruses associated with outbreaks occurring in the U.S. and other countries using MMR belong to genotype groups B, C, D, G, H and I.
The researchers concluded in 2008:
That outbreaks have recently occurred in populations with more than 95 percent 2-dose vaccine coverage strongly suggest that long term prevention of mumps outbreaks with use of current vaccines and vaccination schedules may not be feasible.11
2018: Mumps in Highly Vaccinated U.S. College Students
In 2018, an analysis of a mumps outbreak in 2015-2016 at the University of Iowa and surrounding community found that of 453 cases in the country, 66 percent occurred in university students, primarily undergraduates, who were highly vaccinated: 86 percent had 2 MMR doses and 12 percent had 3 MMR doses. Researchers stated;
One-third of cases among students interviewed reported contact with someone who was ill with mumps. Though many reported either face-to-face contract or direct saliva contact with a person who had mumps, the true contact rate may be underestimated due to contact with asymptomatic cases and a reluctance to report close contact.
MMR Vaccine: A Universal Failure?
In 2016, researchers in the Netherlands reported that during recent genotype G mumps outbreaks worldwide, most mumps patients with symptomatic or asymptomatic mumps infections had received 2 doses of MMR vaccine during childhood.12
Two years later, Italian researchers published a review of 15 years of published studies on mumps vaccine entitled “Mumps Outbreaks: A problem in need of solutions.”13 They concluded:
Prevention of mumps remains an unsolved problem. Available vaccines are effective but the protection they evoke declines over time. The use of booster doses can control outbreaks but it is not precisely defined whether they can prevent them. The rapid decline of antibody levels could limit the impact of the introduction of a third dose in the recommended vaccine schedule. Furthermore, in most of the areas, mumps viral strains that are genetically different from those include in the vaccines are emerging and this may favor immune escape.
The measles vaccine in MMR is experiencing similar problems with failures among vaccinated persons: waning immunity; vaccine strains that do not match wild-type strains; and asymptomatic infections in vaccinated children and adults that are not being identified or reported.14
From mumps to measles outbreaks in highly vaccinated populations, MMR is beginning to look a lot like a universally failed vaccine.
This article or commentary provides referenced information and perspective on a topic related to vaccine science, policy, law or ethics being discussed in public forums and by U.S. lawmakers. The websites of the U.S. Department of Health and Human Services (DHHS) provide information and perspective of federal agencies responsible for vaccine research, development, regulation and policymaking.
1 Scott B. Mumps Outbreak Near University of Florida. Fox 35 Orlando May 30, 2019.
2 Crawford L. 24 cases of the mumps confirmed at the University of Florida. WTSP News June 4, 2019.
3 CDC. Mumps Cases and Outbreaks. June 3, 2019.
4 CDC. Mumps vaccination. Mar. 8, 2019.
5 CDC. Measles Cases and Outbreaks. June 3, 2019.
6 CDC. Mumps Cases and Outbreaks. June 3, 2019.
7 CDC. 2018 National Notifiable Infectious Diseases.
8 CDC. Mumps Outbreak Articles. Mar. 15, 2019.
9 CDC. Mumps: Clinical Features. Epidemiological Prevention of Vaccine-Preventable Diseases. 13th ed. Washington, D.C. Public Health Foundation 2015.
10 Dayan GH, Rubin S. Mumps Outbreaks in Vaccinated Populations: Are Available Mumps Vaccines Effective Enough to Prevent Outbreaks? Clin Infect Dis 2008; 47(11): 1458-1467.
12 Hulscher HI, Schurink TM et al. Mumps-specific cross-neutralization by MMR vaccine-induced antibodies predicts protection against mumps virus infection. Vaccine 2016; 34(35): 4166-4171.
13 Principi N, Esposito S. Mumps outbreaks: A problem in need of solutions. J Infect 2018; 76(6): 503-506.
14 Fisher BL. What Is Going On With Measles? The Science and Politics of Eradicating Measles. NVIC Newsletter May 25, 2019.