On May 23, CDC posted Announcement—London 2012: Olympic and Paralympic Games on its Travelers' Health web section. The announcement advises U.S. travelers to the 2012 Olympic Games (July 29–August 12) and 2012 Paralympic Games (August 29–September 9) to plan ahead while in the U.S. and to take precautions after arriving in London. Heading the list of CDC travel tips is this advice on vaccination:

Make sure you are up to date on your routine vaccines. Most people get these before they start school. The vaccine that protects against measles is especially important. There’s a large measles outbreak in Europe, and a lot of unvaccinated American travelers were infected with measles in 2011.

The announcement includes many other travel tips and links to useful travel websites.

Source: CDC. Announcement-London 2012: olympic and paralymic games. Accessed June 2, 2012.