In February, a passenger who had measles was on an international flight that landed at SFO. The person who had measles during the time of the flight was a Santa Cruz County resident. Since then, two additional passengers who were exposed to measles on that flight have become sick with measles: one was a San Francisco resident and the other was a Santa Clara County resident. The general public is at very low risk of measles as a result of these cases. No other passengers contracted measles as a result of exposure on that flight. The flight was more than three weeks ago. Measles develops within 21 days of exposure. Public health investigators have not identified any evidence indicating that measles is spreading within the impacted counties. Making sure you have all your immunizations is especially important for travelers, because measles is circulating in many countries outside the United States. Early immunization with MMR vaccine is recommended for infants ages 6-11 months before going on an international trip.