Now a new study in the Lancet medical journal finds the vaccine may be linked to reduced cervical abnormalities.
Researchers say, since that program started, the rate of cervical abnormalities, or HGA, was cut in half in women under 18. There was no drop in rates in older women.
The CDC warns these results should be viewed with caution. Doctors add, it will take decades to show a true reduction in cervical cancer.