In clinical research trials, scientists study the safety of a drug, medical device or vaccine and its efficacy. Efficacy can be thought of this way:
Under the ideal situation where a specific type of person uses the drug/device exactly as the researcher/developer intended at exactly the right dose, efficacy measures the extent to which the medicine or device does what the developer thought it would do. Safety is more obvious. The goal in the safety trial is for the drug or device not to kill anyone. Nor should it cause serious harm or side effects that are greater than the positive benefit.
Clinical trials tell us a lot about both safety and efficacy. But they are better at uncovering side effects that the greater public might experience than at confirming effectiveness.
When you or I take the drug or use the device under less than ideal situations, its effectiveness is considered. Drugs and medical devices continue to be studied for several years after they come to market. They are studied in the overall population.
Last week I completed a short continuing medical education activity (CME) on HPV vaccines. It was offered through Medscape. I learned that the real life common side effects occur in a small number of persons and are not severe. They include same day fainting or dizziness and delayed skin rash. In the same activity, I learned that there is no evidence that one cervical cancer case has been prevented by this vaccine. That was a curious point to make and it wasn't followed up with a review of that research. However, Medscape is a peer reviewed website so I feel that the statement was true.
My take away was that the vaccine is not harmful, but also may not be effective. It is likely that the efficacy (confirmed in the clinical trial) was based on the age of the person receiving the vaccine and that they received all three doses.
Whether or not you choose to get this vaccine, if you are a woman, a pap smear every 3 to 5 years is necessary. The pap smear can detect changes in the cells around the cervix which might indicate a pre cancerous condition.