The most frequent reasons given

The most frequent reasons given by parents for not vaccinating their teens with Tdap/Td and MCV4 in 2010 were similar and consistent over the three years but were more diverse and changed significantly when it came to the HPV immunization: 9% said it was not recommended; 17% said it was not needed/not necessary; 16% cited safety concerns/side effects; 11% said it was because their daughter was not sexually active.

(A study co-author has done work for Merck, which makes an HPV and Td vaccine, but the study was funded through a grant from the Department of Health and Human Services.)

Although lack of sexual activity declined as a key reason for parents' rejection of the vaccine (down from 14% in 2008), it "again points to parental misunderstanding about HPV vaccination" and suggests that more work is needed to help some parents understand the vaccination, says Gregory Zimet, professor of pediatrics and clinical psychology at Indiana University School of Medicine. He was not involved in the study

"It's particularly concerning that parental worries about safety have increased, given that evidence for the safety of HPV vaccination has increased over the same time period," says Zimet. "In fact, the evidence is overwhelmingly persuasive that HPV vaccines are quite safe

The first HPV vaccine was licensed in 2006, and even then "there was very strong evidence that it was safe," says Jessica Kahn, professor of pediatrics at Cincinnati Children's Hospital Medical Center. She was not involved in the study. That evidence "only continues to increase as tens of millions of doses have been administered and no evidence of safety concerns has emerged," says Kahn.