By next year, doctors expect to have a vaccine that 100% effective against two strains of the human papilloma virus (HPV) that causes most cases of cervical cancer. It’s very common to be infected with HPV, but the infection usually clears on its own. If it persists, it can cause changes in the cells of the cervix, which can lead to cancer. The vaccine may work best if given to adolescents, but it will be years before we know whether it gives long term protection. So smears are still essential.