Those data also reveal that many infants fall just one doctor's visit short of receiving all of their scheduled vaccines. If these infants had received their final shots, America would have exceeded the goal of 90 percent immunization in 1999. The actual immunization rate that year was just more than 73 percent.

Several analyses of the NIS data are published in a supplement to the May issue of the American Journal of Preventive Medicine.

Overall, 73.2 percent of American children received a full series of vaccinations, according to an analysis of NIS data.

That study revealed that 73.5 percent of the children who had not received a complete vaccination series needed only one more visit to finish out their series of shots, and most needed only one more shot to be fully immunized, say Elizabeth T. Luman and her associates at the Centers for Disease Control and Prevention (CDC).

This was reflected in the finding that children who were fully vaccinated averaged six immunization visits, while children who didn't receive all their shots averaged five visits.

Vaccination coverage increased with increasing numbers of visits. In fact, the group of children who had nine visits approached the Healthy People goal, with 89.7 percent receiving all their shots.

Vaccines come with recommended schedules designed to optimize immune response to the shots. However, doctors may not be taking full advantage of the flexibility of these recommendations, which would allow them and parents various options for completing the vaccinations on time, the researchers say.

"One potential strategy is to administer at each health encounter as many vaccinations as are age- and interval-appropriate, thus preventing missed opportunities for vaccination," Luman says. "Others advocate spreading vaccinations over more than the minimum number of visits."

The researchers note that while infants could receive as many as five vaccines in one visit, only 3.3 percent of infants do, likely due to the concern that too many shots will overburden the infant's immune system. With the recent addition of four doses of pneumococcal vaccine, however, this will play an increasingly important role in childhood vaccination.

Among African-American children, the primary reason for inadequate vaccination coverage does not appear to be too few visits, according to another study using NIS data.

Of the more than one-quarter of black infants who do not receive all their immunization shots, 63.7 percent had had enough visits. As in the previous study, most of the children who failed to receive the full vaccination series also could have completed the series in just one more visit, and 40.3 percent needed only one more shot, says Danni Daniels and CDC colleagues.

"Our findings suggest that most of the undervaccination was not a result of limited access to care, but rather a result of missed opportunities. If providers who treated these African-American children had taken advantage of every vaccination contact to evaluate vaccination status and administer all needed doses of vaccines, coverage could have been as high as 90.5 percent," they say.

The majority of children in this study had only one vaccine provider, diminishing the likelihood that gaps in record-keeping were to blame.

African-American infants who were not up-to-date with their vaccinations at age 3 months were more likely to end up severely undervaccinated, prompting the researchers to suggest that "providers should evaluate vaccination status at every visit and be alert to children who are not up-to-date at age 3 months."

They also uncovered the disturbing fact that nearly 10 percent of the children did not receive the single dose of measles vaccine recommended at age 12-to-15 months. This may leave 85,000 African-American children susceptible to the disease until as late as school entry.

When it comes to vaccination coverage, the gap between the haves and have-nots remains despite increases in immunization during the 1990s, another analysis of the NIS data shows.

Vaccination coverage for children living above the poverty level rose to 81.4 percent in 1999, while it was about 75 percent for children living near or in poverty. Among children in severe poverty, defined as less than 50 percent of poverty level income, 71.4 percent received all their immunization shots, report R. Monina Klevens, D.D.S., M.P.H., and co-author with Luman of the CDC.

"This study describes persistent undervaccination among children living in poverty, indicating that not all U.S. preschool children were equally protected against vaccine-preventable diseases," they say, adding that the gap in the late 1990s was similar to the gap seen in the early 1990s.

The study also showed that coverage rates among poor children dropped in several cities, including Baltimore, Philadelphia and San Diego. Although the decreases were not statistically significant, they are worrisome because groups of children who are undervaccinated are susceptible to outbreaks and can transmit disease to others in the community, the authors declare.

They also note that this study showed "that children living near poverty had coverage levels similar to children living below poverty. It is reasonable to speculate that these children are underinsured and potentially represent the families of the 'working poor.'"

To help resolve this problem, the investigators suggest that communities identify the bariers poor families face and implement strategies to address those barriers.

(Editor's Note: For copies of the article, contact the Center for the Advancement of Health at info@cfah.org).

[Contact: Ira R. Allen]

23-Apr-2001