The Centers for Disease Control and Prevention (CDC) has released a report urging people to get vaccinated after reported measles cases in the U.S. reached a 20-year high - and it’s only May.

Between January 1 and May 23 of this year, 288 cases of measles in the U.S. were reported to the CDC, making it the largest number of reported cases within the first 5 months of the year since 1994. Why are we seeing this surge in measles? According to the CDC, it’s mostly because of international travel by unvaccinated individuals. 97% of the cases so far were so called “importations”, where individuals have caught the disease from another country and brought it back. Furthermore, 90% of the infected individuals were either unvaccinated or did not know their vaccination status. 85% of the unvaccinated individuals said that they remained unvaccinated because of personal, philosophical or religious reasons.

“The current increase in measles cases is being driven by unvaccinated people, primarily U.S. residents, who got measles in other countries, brought the virus back to the United States and spread to others in communities where many people are not vaccinated,” says Dr. Anne Schuchat, director of CDC’s National Center for Immunizations and Respiratory Diseases. “Many of the clusters in the U.S. began following travel to the Philippines where a large outbreak has been occurring since October 2013.”

Measles is not a harmless disease. It can have serious complications and is very contagious. Around 30% of measles cases will develop complications such as pneumonia and diarrhea and 1 child in every 1,000 will develop encephalitis (inflammation of the brain). Although many countries have measles vaccination programs, the disease is still common in various parts of the world. It is estimated that 20 million people each year get measles; 122,000 of these individuals will die of the disease.

Measles is a vaccine preventable disease. There is an overwhelming amount of evidence that demonstrates both the safety and the efficacy of the MMR vaccine. The CDC recommends two doses of this vaccine starting at the age of 12 months, but any individuals travelling internationally can receive the vaccine after the age of 6 months prior to departure. The CDC strongly recommends vaccination to anyone, regardless of whether they are intending on leaving the country, before the summer travel season approaches.