Some parents have complained that the vaccination program -- which will initially target 600,000 girls starting at age 12 --- could put their daughters at risk of extreme reactions or make them more inclined to have sex at an early age, the Times of London reported Thursday.

The vaccine advisory group Jabs said worried parents have contacted the group with their concerns.

"There is a number of questions we want answered, such as how will the vaccine affect prepubescent girls? There have been only very limited trials. A large number of adverse reactions was reported in the U.S. for the drug they use, such as collapsing, seizures and paralysis," spokeswoman Jackie Fletcher told the newspaper.