While the up-to-date immunizatio

While the up-to-date immunization rates rose for all those vaccines, the proportion of girls fully immunized against HPV (three doses over six months) was substantially lower than the proportion for the other two vaccines.

"You'd expect as people get more familiar with a vaccine that they would actually become more comfortable with it," says Paul Darden, professor of pediatrics at the University of Oklahoma Health Sciences Center and co-author of the study. "That doesn't seem to be the case with HPV," he says.

The findings suggests that additional approaches — from detailed discussions about vaccine safety and effectiveness between parents and doctors to additional "social media sorts of things" — may be needed to improve HPV immunization rates, says Darden.

He and colleagues analyzed data from the parents' report portion of the 2008-2010 National Immunization Survey of Teens, a government phone survey of households with adolescents ages 13 to 17.

It found that as of 2010, 81% of teens had the Tdap/Td vaccines and 63% had the MCV4 vaccine. Only 32% of girls were immunized against HPV.

More recent vaccination data from 2011, released after the new analysis, shows 85% of teens had the Tdap/Td vaccines; 71% had the MCV4 vaccine; and 35% of male and female teens were immunized against HPV.