Overall, young children in the U.S. maintained high vaccination rates in 2012, officials at the U.S. Centers for Disease Control and Prevention said Thursday.
But researchers also said there were 159 reported cases of measles between Jan. 1 and Aug. 24 this year — a higher number than usual — and gaps in immunization appear to be to blame.
The new data were published in two reports included in the latest edition of the health agency's Morbidity and Mortality Weekly Report.
In the first of the two papers, CDC researchers analyzed responses from the National Immunization Survey, which monitors vaccine coverage among children 19 to 35 months of age. The federal government targets 90% childhood vaccination rates. Nationwide, Americans are hitting or exceeding that goal for measles, mumps and rubella; for polio; for hepatitis B; and for varicella (the virus that causes chicken pox). Americans missed targets for diphtheria, tetanus and pertussis, and for Hib and PCV vaccines.
Less than 1% of young children in the U.S. did not receive any vaccinations. In many cases, children who live in families with incomes below the federal poverty level had lower immunization rates than children living at or above the poverty level. Vaccine coverage also varied among states. Alaska had the lowest rate for the combined vaccine series, at 59.5%, while Hawaii had the highest, at 80.2% (California's rate was 66.8%.)
The second report provided additional data on the 159 measles cases reported in 16 states and New York City this year, through August. Almost all of the cases were "import-associated," meaning that they were acquired initally outside the U.S. (where measles has been eliminated). Most of the measles cases occurred in people who were unvaccinated (131) or had unknown vaccination status (15). Among unvaccinated U.S. residents in the group, 92 — or 79% — remained unvaccinated because of "philosophical objections" to the practice.
The statistics sound a warning against forgoing immunizations, the authors wrote.
"The increase in measles cases in the United States in 2013 serves as a reminder that imported measles can result in larger outbreaks, particularly if introduced into areas with pockets of unvaccinated persons," they wrote, making mention of the ongoing outbreak in Texas, among members of a church group that is opposed to vaccination.
Speaking to reporters Thursday, Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the CDC, said that the immunization statistics were "really good results, but there is opportunity for improvement."
Regarding measles, she encouraged more people who can to get their shots.
"We need to stay ahead of this virus," she said. "We need very high rates of immunization to protect the most vulnerable - children too young to be vaccinated and those who can't be vaccinated due to health conditions."