Despite measles having been declared eliminated in the United States 15 years ago, there have continued to be occasional outbreaks of the virus that have raised questions about the virus itself, the medications available to prevent its transmission, and the federal government's role in ensuring that vaccine-preventable diseases, such as measles, do not reestablish themselves in the United States. This report presents basic information about this infectious disease, its history in the United States, available treatments to prevent individuals from contracting measles, and the federal role in combatting measles—from funding, to research, to the authority of the federal government in requiring mandatory childhood vaccinations. According to the U.S. Centers for Disease Control and Prevention (CDC), "measles is a highly contagious virus that lives in the nose and throat mucus of an infected person." It is transmitted through coughing and sneezing, and it can live for up to two hours on a surface or in an airspace where the infected person coughed or sneezed. Someone who is not immunized against measles and comes into contact with the virus has a 9-in-10 chance of becoming infected. Symptoms associated with the measles start to appear approximately 7 to 14 days after a person is infected. Symptoms usually consist of high fever, cough, runny nose, and red/watery eyes. Two to three days after the onset of symptoms, small white spots may appear inside the mouth; a rash typically follows three to five days after symptoms begin. The most common complications from measles include inflammation of the middle ear, pneumonia, and diarrhea. Measles can cause serious illness resulting in hospitalization, and 1 in every 1,000 measles cases may develop acute encephalitis (inflammation of the brain), which could lead to permanent brain damage. Between 1 and 2 of every 1,000 children with measles will die from respiratory and neurologic complications. Those who are most at risk for severe illness and complications from the measles include infants and children younger than 5 years old, adults older than 20 years old, pregnant women, and people with compromised immune systems (e.g., HIV infection, cancer patients). Diagnosed cases of measles were first required to be reported by health care officials in the United States approximately 100 years ago; about 6,000 measles-related deaths were reported each year for the first decade of reporting. In the decade prior to the introduction of the first measles vaccine in 1963, most children got measles while growing up. Each year, approximately 3-4 million people in the United States caught the infection, an estimated 400 to 500 people died, and 48,000 were hospitalized. As recently as 2013, the World Health Organization estimated 145,700 deaths globally from measles. In 1954, John F. Enders and Dr. Thomas C. Peebles collected blood samples from several ill students during a measles outbreak in Boston, MA, in an attempt to create a measles vaccine. By 1963, Enders and colleagues had successfully created a measles vaccine and licensed it in the United States. Today, the measles vaccine is combined with mumps and rubella (MMR) or with mumps, rubella and varicella (MMRV). The Advisory Committee on Immunization Practices (ACIP) and CDC recommend that all children receive two doses of MMR vaccine, the first dose at 12 to 15 months of age, and the second at 4 to 6 years of age. Adults who do not have evidence of immunity (e.g., written documentation of vaccination, laboratory confirmation of measles) are recommended to receive at least one dose of the measles vaccine. Those who should not get the vaccine include anyone who has ever had a life-threatening allergic reaction (e.g., anaphylactic shock) to the antibiotic neomycin or to prior doses of the MMR or MMRV vaccine, pregnant women, and individuals with any type of cancer, HIV/AIDS, or other immune system disease. According to the CDC, the risks associated with the MMR vaccine "causing serious harm, or death, is extremely small" and receiving the vaccine "is much safer than getting measles, mumps, or rubella." However, as is the case with every medication, the MMR/MMRV vaccine is not 100% safe. It can result in what CDC characterizes as "mild problems," such as fever (1 out of 6 people) or mild rash (1 out of 20 people); "moderate problems," such as seizure caused by fever (1 out of 3,000 doses) or temporary joint stiffness or pain, mostly in teenage or adult women (up to 1 out of 4); and "severe problems," such as serious allergic reaction (less than 1 out a million doses) or deafness. The rarity of these severe problems makes it difficult to ascertain whether they are caused by the vaccine. It should be noted that among the issues that has resulted in pockets of lower rates of MMR/MMRV vaccination have been concerns over the safety of the measles vaccine itself, in particular concerns that the vaccine may cause autism. While the perception is real and may be influencing some parent's decisions to vaccinate their children, the scientific link between autism and the MMR vaccine has been studied extensively and has overwhelmingly been found to be unsubstantiated. According to data published in CDC's Morbidity and Mortality Weekly Report (MMWR), in 2013 (the year for which most recent data are available) "the overall national coverage for MMR vaccine among children aged 19 - 35 months was 91.9%." However, MMR vaccine coverage levels vary by state. According to the CDC, "in 10 states, 95% of the children aged 19–35 months in 2013 had received at least one dose of MMR vaccine, while in 17 other states, less than 90% of these children were vaccinated against measles." The MMWR article also observes that "pockets of unvaccinated people can exist in states with high vaccination coverage, underscoring considerable measles susceptibility at some local levels." CDC has noted that MMR vaccination rates among children 19 – 35 months have exceeded 90% since 1996. What has changed in recent years is the number of measles importations into the U.S. due to the continued high rates of measles in some parts of the world combined with pockets within the U.S. where vaccination rates are low. In tandem, despite an overall high rate of immunization, these trends continue to put individuals who cannot or will not get vaccinated at greater risk for the disease. The President's FY2016 budget request for the CDC reports that "from January 1 to November 29, 2014, CDC received reports of 610 measles cases from 24 states in the United States. This is the highest number of cases reported in the United States, including the largest single measles outbreak, since the Vaccines for Children (VFC) Program was established in 1994." Thus far in 2015 (through January 30), CDC has received reports of 102 measles cases located in 14 states. Most of the 102 cases—81 people from California and 13 from six other states—are considered to be part of a large, ongoing outbreak linked to an amusement park in California, and about half the patients were unvaccinated or did not know their vaccination status. At present, only one company is licensed to sell measles vaccine in the United States: Merck & Co., Inc., based in Whitehouse Station, NJ. According to the U.S. Food and Drug Administration, Merck is licensed and approved to sell two vaccines that contain the measles vaccine—one is the Measles, Mumps and Rubella Virus Vaccine, Live (known as MMR II), and the second is Measles, Mumps, Rubella, and Varicella Virus Vaccine Live (known as ProQuad). According to Merck's financial filings with the U.S. Securities and Exchange Commission, global revenue from the sale of ProQuad in 2013 (the most recent year for which annual sales data are available) was $314 million; revenue from the sale of MMR II was $307 million for the same year. For the first nine months of 2014, revenue from the sale of ProQuad was reported to be $278 million and revenue from the sale of MMR II was $249 million. The role of the federal government in vaccine policy, particularly in the development of guidelines for when to administer specific vaccines (and when not to) and to what populations is extensive. The federal government also has a major role in the purchase and distribution of vaccines, particularly childhood vaccines. However, the role of the federal government is much more limited and constrained in its ability to mandate the use of specific vaccines by individuals—this responsibility rests primarily with state and local officials. As mentioned earlier, the federal government's role in making evidence-based recommendations and guidance on the use of vaccines by different population groups is significant. The CDC's ACIP is the main group within the federal government charged with developing "recommendations on how to use vaccines to control diseases." The federal government has a robust capacity for monitoring vaccine usage, particularly the potential for adverse events. The system in place for this task is the Vaccine Adverse Event Reporting System (VAERS), operated jointly by the CDC and the FDA. Both vaccine manufacturers and healthcare providers must report adverse events through the VAERS system, whereas others (e.g., consumers) may do so voluntarily. The President's FY2016 budget request included $4.1 billion for the Vaccines for Children Program (VCP), which provides "vaccines to children whose parents or guardians may not be able to afford them," including vaccination against the measles. Funding for the program is allocated through the Centers for Medicare & Medicaid Services to the CDC. In addition to the VCP is CDC's Section 317 immunization program, which is funded by annual discretionary appropriations and provides grants to states, territories, commonwealth trusts, and several cities for vaccine purchase and programs (e.g., outreach and disease surveillance).