While some may be concerned that the vaccine doesn't protect against enough strains of human papillomavirus, which could render it ineffective, that's simply not the case. "The current vaccine protects against all of the high-risk HPV viruses, those which can cause cancer," Dr. Chalas said. "While there are more than 100 HPV viruses, and the most recent vaccine in nonavalent — which means it covers against the nine most common — it turns out that when you get that vaccine there is crossover activity for others, and it protects against more than the nine viruses."