Ninety percent of measles cases so far this year have affected those who are unvaccinated or individuals who were unsure of their vaccination status, according to Schuchat.
Incidences of whooping cough are also growing. Already this year, 8,521 cases have been reported, with most of them in California, Ohio, and Texas. That represents nearly a 50 percent increase from April, when the CDC announced that pertussis cases had risen 24 percent over the same period in 2013.
Like measles, pertussis can lead to pneumonia and can be deadly in babies. Because the disease is highly contagious, those who are not vaccinated can easily pass it on to infants and to other unvaccinated individuals.
Overall, Schuchat said the country is doing relatively well in vaccinating children. Ninety-nine percent of American children have received at least one vaccination, though the number of children who are fully vaccinated is much smaller. Only 68.4 percent of children between 19-35 months had received a full combination of vaccinations in 2012.
The numbers also vary by disease. Between 2008 and 2012, the number of children between 19-35 months old who received all four dosages of the pertussis vaccine declined 2 percentage points, to 82.5 percent. The numbers for the MMR vaccine were better, falling only 1 percentage point during the period to 90.8 percent.
Although the national average of individuals who have requested nonmedical exemptions for vaccinating their children in the United States has remained low, there are communities in which anti-vaccination sentiment is growing. And that puts those who medically cannot be vaccinated, or are too young, at greater risk.
In Oregon, in particular, nearly 7 percent of kindergartners last year were not vaccinated for philosophical and religious reasons. In Idaho, Michigan, and Vermont, more than 5 percent of kindergartners avoided vaccination for nonmedical reasons. Outbreaks in those communities could spread easily and endanger children across those states.
Some religious communities, including the Amish, oppose vaccinating on ideological grounds. But there are also low-information smear campaigns being run across the country encouraging parents not to vaccinate their children. Notably, actress Jenny McCarthy became a major opponent of vaccines, linking them, falsely, to her son's autism in numerous media appearances and in an accompanying book. Her then-boyfriend, actor Jim Carrey, made similar arguments, bringing more celebrity to the cause.
"We know there are communities where large numbers of individuals have decided not to be vaccinated," Schuchat said, but added that although a number of parents have objected to vaccination on philosophical, not religious grounds, the supposed link between autism and vaccination hasn't resulted in statistically significant uptick in unvaccinated children.
For now, the CDC is pushing even harder for children and adults to get vaccinated, and urging those who aren't sure about their status to get an additional vaccine. That way, Schuchat hopes, they can contain the problem. "This year we are breaking records for measles," she said, "and it's a wake-up call, because we don't have to let this get even worse."
Stephanie Stamm contributed to this article