The Importance of MMR Immunization in the United States Olivia Perrone, MD, H. Cody Meissner, MD Despite the established safety and efficacy of the measles-mumps-rubella abstract vaccine after almost 50 years of widespread use, the United States is encountering higher levels of measles and mumps disease than has occurred for years. Return of disease threatens the health of those who remain unimmunized by choice as well as those who are immunized appropriately but experience loss of vaccine-induced immunity. The solution to continued threats of illness caused by these untreatable but readily preventable diseases is compliance with recommendations for administration of the measles- mumps-rubella vaccine. Here we examine trends in the epidemiology of measles, mumps, and rubella in recent years and consider the consequences of loss of protective immunity within our country. Department of Pediatrics, School of Medicine, Tufts University and Tufts Medical Center, Boston, Massachusetts Growing concern among health care ∼97% effective in prevention of clinical Drs Perrone and Meissner conceptualized and designed the study, drafted the initial manuscript, professionals and the public regarding disease and is considered to provide fi 2 reviewed the revised manuscript, approved the nal the severity and the contagiousness of lifelong protection against rubella. In manuscript as submitted, and agree to be measles and mumps, 2 previously view of the availability of MMR, a safe accountable for all aspects of the work. controlled diseases in the United States, and effective vaccine, why does disease DOI: https://doi.org/10.1542/peds.2020-0251 has focused attention on the role of the still occur, and what can be done to Accepted for publication May 5, 2020 measles-mumps-rubella vaccine control the spread of measles, to (MMR). The number of reported control the outbreaks of mumps, and to Address correspondence to H. Cody Meissner, MD, Department of Pediatrics, School of Medicine, Tufts measles, mumps, and rubella cases sustain the elimination of rubella? University and Tufts Medical Center, 800 Washington decreased by .95% after introduction St, Boston, MA 02111. E-mail: cmeissner@ of each monovalent vaccine, yet disease tuftsmedicalcenter.org continues to occur nearly 50 years after MEASLES PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, the 3 vaccines were combined into Before measles vaccines were licensed 1098-4275). a single trivalent vaccine in 1971. in 1963, childhood infection with Copyright © 2020 by the American Academy of Measles occurs mainly among measles was nearly universal, resulting Pediatrics unimmunized people exposed to in an estimated 3 to 4 million cases FINANCIAL DISCLOSURE: The authors have indicated fi a contagious traveler who arrives from annually (the birth cohort), .500 they have no nancial relationships relevant to this article to disclose. a country outside the United States deaths, and thousands of cases of 1,2 FUNDING: where measles virus is circulating. measles-associated encephalitis in the No external funding. Mumps outbreaks occur after exposure United States.1 After licensure of the POTENTIAL CONFLICT OF INTEREST: Dr Meissner fi to an index case in settings where first measles vaccines, the incidence of serves as ex-of cio to the Committee on Infectious Diseases, is a member of the National Vaccine people have close, prolonged contact, disease declined rapidly. By 2000, the such as universities or close-knit Advisory Committee, is a member of the Vaccine and United States was certified to be free of Related Biological Products Advisory Committee, and communities, and may or may not have measles, meaning that after is chair of the Vaccine Injury Compensation Program; 2–4 received 2 doses of MMR. The importation of a case, no continuous and Dr Perrone has indicated she has no potential fl attenuated rubella virus contained in transmission occurred for at least 12 con icts of interest to disclose. MMR (Wistar RA 27/3) is more months. Between 1997 and 2013 the effective at inducing protective incidence of measles remained To cite: Perrone O and Meissner HC. The immunity than the measles or mumps remarkably low at ,1 case per 1 Importance of MMR Immunization in the United States. Pediatrics. 2020;146(2):e20200251 vaccine strains, and a single dose is million population.1 Starting in 2014, Downloaded from www.aappublications.org/news by guest on October 4, 2021 PEDIATRICS Volume 146, number 2, August 2020:e20200251 SPECIAL ARTICLE the number of cases increased, and in because of high 2-dose immunization among children who experience 2019, .1250 cases of measles were rates of MMR (that results in high measles than among children who are reported, representing the highest rates of immunity in the community) not infected. This has been attributed number in 17 years.5 Approximately and the rapid implementation of to suppression of innate and adaptive 90% of reported cases occurred control measures from state and local immunity that is associated with among people who were health departments. However, these natural measles virus infection.12 unvaccinated (70%) or whose control measures are costly and draw Some immunologic abnormalities vaccination status was unknown resources away from other critical resolve soon after infection, but (20%).5 public health responsibilities.8 epidemiological studies demonstrate a strong association between measles In the United States, a single dose of In the absence of antiviral therapy, virus infection and increased a measles-containing vaccine treatment of measles consists of morbidity and mortality for months administered at 12 months of age has management of dehydration and to years after infection. In recent a vaccine effectiveness of ∼93% (and nutritional deficiencies (including reports, authors describe immune 97% when administered at vitamin A) and antimicrobial therapy abnormalities that appear to explain 15 months of age). Primary measles if secondary bacterial infections this increased risk of infection after vaccine failure (lack of occur. Approximately 30% of – recovery from measles.13 15 During seroconversion) occurs in ∼2% to 5% reported measles cases result in one an outbreak of measles in the of vaccine recipients who receive 1 of the following complications: Netherlands, unvaccinated children dose of the vaccine. Primary vaccine diarrhea, otitis media, pneumonia, were evaluated before measles failure may be caused by passive and less commonly, acute infection and again 2 months after antibodies in the vaccine recipient at encephalitis, degenerative neurologic recovery. Results revealed an the time of immunization (such as disease (subacute sclerosing impaired adaptive immune response, residual maternal antibodies), panencephalitis [SSPE]), or death.1 as evidenced by an 11% to 73% loss a damaged vaccine, or incorrect SSPE is an invariably fatal, persistent of antibody repertoire, after measles records (ie, administration of the viral infection of neuronal and glial infection. This appears to be incorrect vaccine). Secondary measles cells caused by a defective virus that secondary to measles virus vaccine failure (waning antibody occurs after a wild-type measles replication in and destruction of both concentrations to unprotective levels infection, particularly among children naïve and memory B cells, cells after an initial response) seldom who are infected in the first few years responsible for production of occurs. More than 98% of people who of life. Reports from the prevaccine circulating and secreted antibodies. receive $2 doses of a measles- era suggested rates of SSPE of 5 to 10 This loss of humoral immunity leaves containing vaccine, according to the cases per 1 million measles cases.1,9 children at an increased risk for recommended immunization This figure is considered now to be an infection from pathogens to which schedule, develop serological underestimation because an average they previously had been immune evidence of immunity.1 The second of 6 to 10 years occurs between the because of infection or vaccination. MMR dose is not a booster dose; measles infection and the onset of Recovery of lost immunity was rather, it is intended to induce symptoms of SSPE, making an restored after reexposure to immunity in the small number of association difficult to discern. In pathogens. Remarkably, despite this people who do not develop protective studies after the 1989–1991 measles immunosuppression, lifelong immunity after the first dose. outbreak in the United States and immunity to measles develops among Europe, authors report that the rate The number of measles cases survivors of acute measles infection. of SSPE is more common than occurring in the United States in Measles vaccination is not associated estimated previously, at least 1 case a given year is determined by 2 with the immunologic deficits of SSPE per 5000 measles cases, and factors: first, the number of travelers associated with wild-type measles is perhaps as common as 1 case per who become infected abroad and infection. 1000 measles cases among children travel to or return to this country infected in the first year of life.10,11 In while contagious; and second, the The consequences to a community countries where appropriate measles number of susceptible people who that does not maintain vaccine- immunization programs have been are exposed to the traveler.6,7 Clusters induced protective immunity (herd established, SSPE is nearly of disease are more likely to occur in immunity) to measles can be undetectable. communities with pockets of dramatic. In September 2019, several unvaccinated people. The majority of In reports from countries in Africa cases of suspected measles were importations have not resulted in and elsewhere, authors describe reported in the Samoan islands, and larger outbreaks in the United States higher morbidity and mortality rates by October 2019, a national measles Downloaded from www.aappublications.org/news by guest on October 4, 2021 2 PERRONE and MEISSNER outbreak was declared. By January 7, MMR confer long-lived immunity others at increased risk of 2020, a total of 5655 cases were and meet the CDC definition of exposure do not have written reported in the Independent State of immune.