Measles is still very rare in the United States, but most cases involved either someone who was not vaccinated or whose status is unknown.
Across the United States, the incidence of measles remains very low; however, failure to vaccinate could be the primary driver of measles transmission, according to a study JAMA.
The study, led by Nakia S. Clemmons, MPH, of the CDC, examined the annual incidence of measles in the United States from 2001 to 2015. They discovered that during that time period, the rate of measles in the United States remained "extremely low" with a rate of 0.39 cases per million population.
This figure is significantly lower than the prevalence of measles worldwide, which is thought to be 40 cases per million in the population, according to a JAMA news release announcing the study's findings.
Of the 1,789 cases of measles that were reported among U.S. residents during the study period, most cases either involved an unvaccinated individual (69.5%) or individual where the vaccination status was unknown (17.7%), according to the study.
The incidence of measles was highest for infants between the ages of 6 and 11 months. This group was found to have an incidence per million population of 5.44, while those between the ages of 12 to 15 months had an incidence rate of 5.38. The incidence rate began declining after 16 months of age in the study population.
The study's authors noted that this declining incidence with age, combined with other study findings such as the high proportion of measles cases occurring in unvaccinated individuals, suggests that a primary driver of measles transmission may be a failure to vaccinate, rather than an indication of the vaccine's performance.
They believe their research further demonstrates the need and value of the measles vaccine.
The measles vaccine continues to have a substantial impact across the globe. According to information from the Measles and Rubella initiative, it is estimated that, by 2020, the measles vaccine will have saved more lives than all other vaccines combined. The initiative estimates that due to its low cost and effectiveness, the rate of return is $58 for every $1 invested in the vaccine.
The Measles and Rubella Initiative is a collaborative effort by organizations, including the American Red Cross, United Nations Foundation, CDC, UNICEF, and the World Health Organization, that strive to ensure that no child dies from measles or is born with congenital rubella syndrome.