Measles cases have soared to a 20-year high in the US, with 288 cases reported since the beginning of the year — the most in a five-month period since 1994. Though measles was declared to be eliminated from the US in 2000, importation of the disease has continued, and in all cases this year where the source of infection could be determined, it was seen as stemming from international travel.

Most patients weren't vaccinated for religious, philosophical, or personal objectionsThe US Centers for Disease Control and Prevention pins the striking rise in measles cases on unvaccinated people, who make up at least 69 percent of the reported cases. (In 20 percent of cases, the person's vaccination status was unknown. In only 10 percent of cases was the person actually known to be vaccinated.) Some of the unvaccinated people were too young to receive vaccination or said that they had missed opportunities to be vaccinated. But the vast majority, 85 percent, had refrained from vaccination because of religious, philosophical, or personal objections.

"The current increase in measles cases is being driven by unvaccinated people, primarily US 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," assistant surgeon general Anne Schuchat says in a statement.

Though measles is reaching a relative peak in the US, it's still far lower in the United States than elsewhere across the globe. There's estimated to be around 20 million annual measles cases worldwide and about 122,000 deaths stemming from it.

Still, the rise in the United States is sharp. The CDC reported that measles cases had spiked in 2013 too, and 2013 saw only 175 confirmed cases in total by early December. In that report too, the CDC said a failure to vaccinate was the issue, with 98 percent of cases being in unvaccinated patients.

Elsewhere in the world, widely disproven concerns that vaccines are linked to autism are said to have been the cause of measles outbreaks. At least one isolated instance of this led to a small outbreak in Texas last year, though the CDC doesn't break down the exact reasons why measles patients turned down vaccination.