The U.N. children's agency, UNICEF, says 1.4 million children die each year from diseases that could be prevented by vaccination.

A UNICEF report released Thursday says one in four infants is still at risk from vaccine-preventable diseases. Each year, 27 million children are not properly immunized.

The latest UNICEF report, titled "Progress for Children", shows more than half the 191 U.N. member states are meeting child vaccination goals. Nevertheless, 1.4 million children under five die needlessly each year from measles, whooping cough, tetanus and other preventable diseases.

UNICEF's Immunization Director Dr. Peter Salama says past gains in immunizing vulnerable groups have been partially lost. Part of the reason is complacency after the success of early campaigns. But in some places, particularly in Africa, he says cultural resistance, armed conflicts and weak health-care systems pose additional obstacles.

"The Democratic Republic of Congo is a classic example, where sustained civil war, particularly in the eastern part of the DRC, has led to our inability to deliver any health interventions in that part of the world," he said. "In other countries such as Nigeria it's a combination of factors, including a real lack of understanding in some communities, including the lack of trained health workers, some basic misconceptions about vaccinations."

But Dr. Salama says success stories in countries as diverse as Somalia and Afghanistan show that, in his words, "you can do it even when the odds are against you".

"Somalia and Afghanistan are probably two of the most difficult countries in the world to conduct immunization campaigns but we've done it in those countries consistently and with very high coverage," added Dr. Salama. "So it shows you that in those remote areas with a lot of government commitment of the international partnerships we can reach most children around the world."

The UNICEF report points to other success stories in resource-poor countries. In Eritrea, for instance, routine immunization coverage went from 18 percent in 1990 to 84 percent in 2003. Niger jumped from 25-percent to 64-percent, and Uganda moved from 52 percent to 82-percent in that same period.

UNICEF Director Ann Veneman says $1 billion a year is now being spent on child immunizations, and another one billion dollars is needed to reach goals set by the United Nations.

The United States is the largest financial contributor to UNICEF.