https://www.bmj.com/content/361/bmj.k2059

The reassuring conclusions, based on 26 studies involving 73 428 women, confirmed what the vaccine trials had shown—that these vaccines are a powerful tool in reducing deaths from cervical cancer. They work best if given to young women who are free of HPV at the time of vaccination, almost eliminating cervical lesions, but they also approximately halve this risk in women aged 15-26 who are already infected with HPV.