Letters to the editor; a possible spurious correlation between human papillomavirus vaccination introduction and birth rate change in the United States.

A possible spurious correlation was found between human papillomavirus (HPV) vaccination introduction and birth rate change in the United States. Thus, the effects of HPV vaccination needed to be followed carefully at an international level. The birth rate change in the US might be representative of the trend of the introduction of new contraception methods and advancing maternal age.