Measles

Measles is a highly contagious viral illness characterized by a high fever and rash.

Prevalence
Before a vaccine was licensed in 1963, over 90% of children in the US got measles by the age of 15, and around 500 people died from measles each year in the US. From 2008 through 2017, the number of measles cases reported in the United States each year averaged 180 (about 1 in 1.75 million population) but varied from 55 (in 2012) to 667 (in 2014). Most of these cases were in unvaccinated people.

Transmission
Measles is very contagious, the virus is spread by the tiny droplets relesed 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 virus become infected. A person who has had measles in the past is considered to be immune to measles for the rest of their life.

Symptoms and complications
A fever typically begins 10-12 days after exposure, and increases in stepwise fashion, often reaching 103-105 degrees. Fever is followed by runny nose, pinkeye, and distinctive white spots inside the mouth ("Kopilk spots"). 1-7 days (usually 2-4 days)  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, the following rates of various complications were reported by the CDC.

A degenerative brain condition called subacute sclerosing panencephalitis (SSPE) affects 1 in 25,000 people who get measles. SSPE  typically occurs 6-15 years after a person gets measles, and is usually fatal. Children who get measles at a younger age are more at risk for SSPE, and it is more common in boys than girls.

Prevention
One dose of the MMR (measles, mumps and rubella) vaccine makes 95-98% of children vaccinated immune to measles. Two doses are recommended by the CDC and NHS.