Pressroom

Source: Washington Post

By: Haelle, Tara

06/23/2014

The number of reported measles cases in the United States reached 514 so far this year, the highest level since the disease was declared eliminated in 2000. The measles vaccine is one of the most effective vaccines, and most Americans are immune either because they have had the measles or have been vaccinated against it. One reason why so many people are still being infected may be because of vaccine refusals for religious, philosophical, or personal reasons. However, 10 percent of cases occurred in vaccinated individuals. Researchers in February published a case study about a woman who had been vaccinated against measles, but still contracted the disease and passed it along to four others, two of whom had also been vaccinated. Sometimes, when a person receives a vaccine, their immune system does not create the necessary antibodies to protect against the disease. This is why a second shot of the MMR vaccine is recommended. Antibodies and immunity also can wane over time, as illustrated by the pertussis vaccine introduced in the 1990s, which was partly responsible for the recent increase in U.S. pertussis cases. Since the measles vaccine has only existed for about 50 years, scientists are not sure if its effects can last a lifetime, though recent cases imply that they may not.