At what age is it recommended to start the HPV vaccine series for maximum effectiveness?

The recommendation to start the HPV vaccine series around 12 years old is based on evidence that this timing maximizes the vaccine's effectiveness. This age aligns with the period when individuals are typically beginning to engage in sexual activity, allowing the vaccine to provide protection before they are exposed to the virus.

The vaccine is most effective when administered before the onset of sexual activity because it works by preventing the acquisition of HPV, rather than treating an existing infection. Starting the series at this age also takes into account the immune response, which is strongest in preteens and young adolescents, thereby enhancing the likelihood of developing long-lasting immunity.

While vaccination can be given as early as 9 years old and is also recommended for older adolescents and young adults, initiating the series at around 12 maximizes the opportunity for protection during the critical years when individuals may first become sexually active.