The HPV vaccine requires three injections. If you have the bivalent vaccine, you need to have the second injection after the first injection, and the third injection after the sixth month, so that you can produce effective antibodies to prevent cervical cancer. If one injection is given, antibodies can be produced, but the amount of antibodies is not enough. In addition, the antibodies produced are relatively small and will be gone soon, so it will not work to prevent cervical cancer either. According to the formal injection process of cervical cancer vaccine, for quadrivalent and nine-valent vaccines, you need to have the second injection after two months and the third injection after six months after the first injection.