In 2006, the Federal Drug Administration approved the vaccine Gardasil to prevent infection with the four most concerning types of genital human papillomavirus—types 6, 11, 16, and 18 3. According to the FDA, Gardasil protects girls and women, ages 9 to 26, from genital warts, caused by types 6 and 11; as well as vulvar, vaginal and cervical cancers caused by types 16 and 18. The vaccine also protects boys and men, ages 9 to 26, against infection with genital warts caused by HPV types 6 and 11. However, the Gardasil vaccine may cause serious side effects.

Injection Site Side Effects

Certain side effects are quite common at the site of an injection; these are known as “local” side effects. However, in rare cases—7.5 cases per 100,000 doses of vaccine given—a severe reaction may occur. These more serious reactions include severe pain, inflammation, formation of cysts or formation of an abscess, which is a pus-filled mass that forms at the site of the injection.

Digestive System-Related Side Effects

The digestive system may also be affected by the Gardasil vaccine. The pharmacology database MicroMedex reports that about 7 percent of patients receiving the vaccine will feel nauseous within the first two weeks of getting vaccinated. The Gardasil website as well as the UpToDate medical database both indicate that about 1-2 percent of patients will suffer from vomiting, which may become dangerous if food and water is not able to stay down. Diarrhea can also be a problem, affecting up to 4 percent of people getting the vaccine. As with vomiting, this may not be a significant concern at first, but if the diarrhea is severe, dehydration may occur, which is a potentially dangerous situation. Finally, appendicitis is a very rare but significant side effect that may occur; according to MicroMedex, this potentially life-threatening effect only occurs in 0.3 percent of patients but is important to note because in these cases the appendicitis was considered to be directly related to the administration of the Gardasil vaccine 3.

Central Nervous System-Related Side Effects

The more common central nervous system effects of Gardasil would be more correctly described as irritating, perhaps even debilitating, but probably not dangerous. Specifically, headaches are extremely common effects of the injection, impacting nearly 30 percent of people who receive the vaccine. Fever is another common side effect; however, unless a fever is extremely high, it would likely not be considered dangerous. Interestingly, it is the less-common side effects that are actually more dangerous. According to the Gardasil website, fainting may occur in some people who have received the injection. Because of the potential danger of falling or hitting one’s head, the Gardasil website reminds people that after getting the vaccine, the physician may ask the patient to lie down for 15 minutes, to ensure that a fainting episode won’t occur. Finally, dizziness is another potential side effect that occurs in 1-4 percent of cases; as with fainting, the possibility of a fall makes this side effect a serious one to consider.

Other Side Effects

The medical database UpToDate lists a variety of potentially life-threatening side effects of the Gardasil vaccine. Some of these extremely dangerous effects include blood clots in the legs, known as deep venous thromboses; blood clots in the lungs, known as pulmonary emboli; and strokes. Seizures, kidney failure and a neurologic disease called Guillain-Barré syndrome are also possible side effects. Fortunately, these serious side effects are very rare, occurring in less than 1 percent of patients who receive the vaccine.