Some states have nearly 100 percent immunization rates when kids enter kindergarten, but not Pennsylvania, which ranks near the bottom of lists of vaccine coverage by the Centers for Disease Control and Prevention.
Just over 85 percent of kindergartners have gotten their chickenpox vaccinations, for example, when schools report data to Pennsylvania health officials in October.
But experts at the CDC and the Pennsylvania Department of Health say state rankings aren’t exact comparisons, because states have different methods for collecting the data as well as different standards for how long students can be granted “provisional enrollment” in school while they finish their vaccinations.
“I think there’s a lot of variation in how these data are collected,” said Melinda Wharton, deputy director for the National Center for Immunization and Respiratory Diseases at the CDC.
Some states take a full census of public and private schools, she explained, while others use different sampling methods and sizes.
Heather Stafford, who directs the immunization program at the state’s Department of Health, says another issue is timing.
“If we were to get these reports from school nurses later in the year, like March or April,” she said, “our percentages would be higher closer to the end of the eight-month provisional period.”
She said that many students finish vaccine doses between the time schools report immunizations to the state in October and when the state sends data to the CDC in April.
Pennsylvania verifies its vaccination data by taking a random sample of schools in the spring, she said. Those reports show vaccination rates catching up to the national target of 95 percent, as provisionally enrolled students finish off their vaccines.
Pennsylvania vaccine policy, however, is in some ways less stringent than in states that top the CDC list with the highest vaccination rates.
While all states will grant students medical exemptions, according to the National Conference of State Legislatures, first-ranked Mississippi is the only state in the nation that does not offer vaccine exemptions for religious reasons.
Pennsylvania, meanwhile, is one of 19 states that allow parents and guardians to apply for both religious and philosophical exemptions for their children.
Stafford said that 1.5 percent of kindergartners in the state are exempt for those reasons, and another 0.4 percent of kindergartners forgo vaccines due to medical limitations.
The two states also differ in the grace period they grant students who have started but not yet finished vaccine doses. In comparison to Pennsylvania’s eight-month grace period, Mississippi gives students only 90 days to get their immunizations up to date.