Although there was a spread of measles that was eliminate back in 2009, there is a current measles outbreak in the United States. This is due to unvaccinated people who travelled outside the country, got measles and returns while still contagious.
"Measles is so contagious that if one person has it, 90% of the people close to that person who are not immune will also become infected," said CDC on Transmission of Measles.
The measles virus survives for up to two hours in the air and even on surfaces that are contaminated wherever those that have measles sneezes or coughs. This is added to the fact that those with measles are contagious for around four days before they develop the rash. You don't need to be in direct contact with the patient, you can be infected by simply entering a room that they are in or getting on a vehicle with a patient who has measles.
"Evidence of adequate vaccination for school-aged children, college students, and students in other postsecondary educational institutions who are at risk for exposure and infection during measles and mumps outbreaks consists of 2 doses of measles- or mumps-containing vaccine separated by at least 28 days, respectively. If the outbreak affects preschool-aged children or adults with community-wide transmission, a second dose should be considered for children aged 1 through 4 years or adults who have received 1 dose. In addition, during measles outbreaks involving infants aged <12 months with ongoing risk for exposure, infants aged ≥6 months can be vaccinated." said CDC on Prevention of Measles, Rubella, Congenital Rubella Syndrome, and Mumps, 2013: Summary Recommendations of the Advisory Committee on Immunization Practices.
What do you need to do when a vaccinated child is exposed to measles? Children get their first shot of MMR at 12 to 15 months, and the second shot should be done when they are 4 to 6 years old. It is very easy to see that babies, toddlers and preschoolers who are following the schedule of immunization are not going to be vaccinated fully against measles, even if they are not delaying their schedule or skipping their vaccines.
There are cases wherein children who had their first dose of MMR has a good enough protection, this means that they do not necessarily need an early second MMR dose. That is because the focus of measles outbreak are those who do not have any immunity from the virus, they are the unvaccinated.
So what do you do when your child is unvaccinated and is exposed to measles? If your child is not vaccinated and they are exposed to measles, it is best that you talk to your local health department or your pediatrician about post exposure prophylaxis.
