Both parents and government must do more to ensure timely vaccination of children, a New Jersey doctors' group says, pointing to a new national survey that suggests the state may have dropped from the top 10 in the country to the bottom 10 in less than a year.

"We live in the most urban state in the nation," Robert Morgan, a pediatrician and member of the Medical Society of New Jersey, said in an interview. "When you choose not to vaccinate your child, you are making choices for every other child as well."

It is not clear that the latest National Immunization Survey results in New Jersey accurately reflect actual vaccination rates. The survey, conducted from July 2007 through June 2008, found that 70.5 percent of children in New Jersey had received the standard series of vaccines - down from 80.5 percent during the January-to-December 2007 period. The state's rank plummeted.

Twelve-month results from the rolling survey are reported every six months, and they include a six-month overlap.

Although the decline in New Jersey was steep, small sample sizes in each period for each state produce large margins of error, said Jim Singleton, chief of the U.S. Centers for Disease Control and Prevention's assessment branch, which conducts the survey.

In this case, the margin of error for New Jersey was plus or minus about 7 percentage points in each period - enough to produce an overlap that potentially wipes out the decline.

"What we try to tell the states is that you've got to look at the long-term trend year by year," Singleton said. Over the years, New Jersey's vaccination rates have roughly matched the national average - just over 77 percent.

Pennsylvania's rate in the latest survey rose slightly, to 79.9 percent from 78.8 percent.

The New Jersey Department of Health and Senior Services, which sets policy, but does not administer vaccines, has not yet analyzed the most recent data in detail.

"We're certainly concerned about any decline and are looking into it to better understand the reasons," the department said in an e-mail statement Friday evening.

"One key factor may have been the shortage of pneumococcal vaccine in 2007 and 2008, which affected different states at different times," the statement said, adding that "health-care providers have been working hard since the shortage ended last spring to bring children back in and get them caught up."

The state required the vaccine for enrollment in day care and preschool starting last September, just after the latest survey period.

Meanwhile, the New Jersey Medical Society, seeking a theme to publicize on National Doctor's Day, decided to hold a news conference today about the importance of timely immunization. The survey finding was highlighted in an advance announcement.

Morgan, who is on the faculty at Robert Wood Johnson Medical School and the University of Medicine and Dentistry of New Jersey's School of Public Health, agreed with the CDC that the striking drop picked up in the survey could be a statistical anomaly.

Nevertheless, the pediatrician said, "we know we have a problem in New Jersey." Unlike some states, which have a universal purchasing system for all providers' vaccines, New Jersey (and Pennsylvania) has "a fragmented delivery system," he said.

And parents with no memory of the devastating diseases that vaccines have largely eradicated have developed "a false sense of security" as well as an unfounded fear of side effects, he said.

Morgan pointed to a case last year in which a 7-year-old unvaccinated child from California returned from a family trip to Switzerland with measles. The child then infected others, some infants too young to be vaccinated, during a visit to the doctor; 70 or so people were eventually quarantined in their homes.

Contact staff writer Don Sapatkin at 215-854-2617 or