context: Human papillomavirus ( HPV) is the virus that causes cervical cancer in women and genital warts in men and women. The HPV vaccine effectively prevents infection with the HPV types responsible for most cervical cancers and can also prevent genital warts. HPV vaccination is most effective during childhood or adolescence, but adults can also benefit from the HPV vaccine. HPV infection is extremely common; most sexually active people will be infected with HPV at some point in life. HPV infection usually causes no symptoms, but can cause genital warts and anal cancer in both women and men. HPV can also cause throat cancer. In women, HPV infection can cause cells in the cervix to grow abnormally. In a small fraction of women, these HPV-induced changes will develop into cervical cancer. About 12,000 women are diagnosed with cervical cancer each year and about 4,000 women die from the condition. The HPV vaccine prevents infection by the HPV types responsible for most cervical cancers. Up until 2017, there were two vaccines available ( Gardasil and Gardasil 9). Today, Gardasil 9 is the only available HPV vaccine in the U. S. Gardasil 9 prevents infection by the same HPV types as Gardasil, plus HPV-31, HPV-33, HPV-45, HPV-52, and HPV-58. Collectively, these types are implicated in 90% of cervical cancers. In October 2018, the FDA approved Gardasil9 for women and men ages 27 to 45. HPV vaccines are extremely effective at preventing infection by the HPV types they cover. Getting the HPV vaccine reduces a woman's risk of cervical cancer and precancerous growths substantially. Men cannot develop cervical cancer, but the HPV vaccine may prevent genital warts, penile cancer, anal cancer, and the spread of HPV to sexual partners. Gardasil 9 is approved for males ages 9 through 26. The HPV vaccine does not treat or cure an HPV infection in women or men who are already infected by one of these HPV types. It is an option for all men through age 21, but is recommended for men who have sex with men, transgendered people, or those who have a compromised immune system (including HIV) who are ages 26 and younger. CDC guidelines recommend the two doses of the HPV vaccine. Some adults may have received doses of the HPV vaccine in childhood or adolescence. Re-vaccination in adulthood is recommended if the vaccination schedule was not completed. Certain people should not get the HPV vaccine or should wait before getting it: Anyone who has had a life-threatening allergic reaction to a previous dose of the HPV vaccine Anyone who has had a previous life-threatening allergic reaction to an ingredient in the HPV vaccine Pregnant women Anyone with a moderate or severe illness; people who feel mildly ill may still receive the HPV vaccine. The HPV vaccine is not known to be harmful to pregnant women or their babies. However, until more information is known, pregnant women are advised not to receive the HPV vaccine. Women who are breastfeeding can safely receive the HPV vaccine. The HPV vaccine contains no viruses and is not made from human papillomavirus. The active ingredients in the HPV vaccine are proteins that are similar to those found in the human papillomavirus. Genetically modified bacteria produce the proteins, which are then purified and mixed into a sterile, water-based solution. In clinical trials and in real-world use, the HPV vaccine appears to be very safe. More than 40 million doses of the vaccine -- mostly Gardasil, which was approved in 2006 -- have been given in the U. S. Gardasil 9 was approved in 2014 and is now the only HPV vaccine available in the U. S. From 2006 to 2014, there were about 25,000 reports to the government of HPV vaccine side effects. Over 90% of these were classified as nonserious. The most common side effects of the HPV vaccine are minor: About one in 10 people will have a mild fever after the injection. About one person in 30 will get itching at the injection site. About one in 60 people will experience a moderate fever. These symptoms go away quickly without treatment. Other mild-to-moderate side effects resulting from the HPV vaccine include: Nausea Fainting Headache Arm pain Severe side effects, or adverse events, are uncommonly reported and have included: Blood clots Seizures Guillain- Barre syndrome Chronic inflammatory demyelinating polyneuropathy Myalgic encephalomyelitis/chronic fatigue syndrome) Death Government, academic, and other public health investigators could not identify the HPV vaccine as the cause of any severe adverse event. There were 117 deaths as of September 2015, none of which could be directly tied to the HPV vaccine. The conclusion of public health investigators was that the HPV vaccine was unlikely to be the cause of these events. Such events occur at a certain rate in any group of tens of millions of people. The vaccination before each adverse event seemed to be a simple coincidence.