Measles is a highly contagious, but rarely fatal, viral disease. There were 220 reported cases of measles in the United States in 2011. The Centers for Disease Control and Prevention attributes most of these cases to parents choosing not to vaccinate their children. In recent years, the number of measles cases in the U.S. has increased. According to the CDC, this is due to unvaccinated travelers contracting measles overseas and then spreading the virus when they return to the country.
In 2013, the CDC announced that measles outbreaks were increasing, almost entirely among people who were not properly vaccinated.
Measles is very contagious, the virus is spread by respiratory droplets (when an infected person coughs, sneezes, etc). Measles virus can survive in the air and on surfaces for up to 2 hours, and 90% of non-immune people who are exposed to measles become infected
A fever typically begins 10-12 days after exposure, the fever increases in stepwise fashion, often reaching 103-105 degrees F. Fever is followed by runny nose, pinkeye, and distinctive white spots inside the mouth ("Kopilk spots"). 1-7 days (usually 2-4) after onset of fever, a rash appears at the hairline, this rash spreads over the body and then disappears in the order that it appears, lasting a total of 5-6 days. Peeling skin may occur on those body parts most affected by the rash. From 1985 to 1992 8% of measles cases in the US involved diarrhea, 7% resulted in ear infection, 6% resulted in pneumonia, 0.6-0.7% involved seizures, and 0.2% (1 in 500) were fatal (usually due to pneumonia or encephalitis), according to the CDC.
Acute encephalitis (brain inflammation) occurs in about 0.1% of measles cases (1 encephalitis case per 1,000 measles infections), and is fatal in 15% of cases, with up to 25% of survivors suffering permanent neurological damage. 
One dose of the MMR (measles, mumps and rubella) vaccine is at least 95-98% effective in creating immunity to measles. Two doses are recommended by the CDC. This is a live virus vaccine, and may cause some of the symptoms of measles, mumps, or rubella infections, such as fever, rash, and, in post pubescent females, temporary joint pain. Serious side effects listed by the WHO are as follows(1 in 10 means 1 case of the side effect per 10 doses of vaccine):
Acute arthritis (in teen girls and women): 1 in 10
Febrile seizures: 1 in 2,000 to 3,000
Thrombocytopenia (a blood clotting disorder): 1 in 30,000
Mumps virus meningitis: 1 in 100,000 to 1,000,000
Anaphylaxis (life-threatening allergic reaction): 1 in 285,000 to 1,000,000
Encephalomyelitis (autoimmune brain injury): 1 in 1,000,000