By Harmony Phuong Huynh
Published on June 16, 2011
What is Gardasil?
Gardasil is the first available vaccine against genital human papillomavirus (HPV), the most common sexually transmitted virus in the United States. There are various strains of HPV. Made by the company Merck Inc., the vaccine protects against HPV types 6, 11, 16 and 18 in both males and females (Centers for Disease Control and Prevention, “Human Papillomavirus”; Cerner Multum, Inc.). Gardasil protects both males and females from anal cancer and precancerous lesions caused by those four HPV types. In girls and young women of ages 9 to 26, this vaccine protects against HPV types 16 and 18 that are the cause of nearly 75% of cervical cancer cases, 70% of vaginal cancer cases, and 50% of vulvar cancer cases. In females, Gardasil also protects against types 6 and 11 that are the cause of 90% of genital warts cases. In boys and men of ages 9 to 26, the FDA approved Gardasil for the prevention of genital warts caused by HPV types 6 and 11, which constitute 90% of genital warts cases (Cerner Multum, Inc.; U.S. Food and Drug Administration, “Gardasil”).
It is important to note that Gardasil may not completely protect anyone, nor has it been shown to protect against diseases associated with the other 26 or more sexually transmitted HPV types or against diseases not caused by HPV. This vaccine does not prevent all cervical cancer cases, making it crucial for women who have (or have not) been vaccinated to continue routine cervical cancer screenings, such as annual pap smears. In addition, Gardasil is not a treatment for cancer or genital warts and is not effective for those who already been infected with HPV (Cerner Multum, Inc.).
Gardasil (see Figure 1) is injected into the upper arm or upper thigh muscle and is administered in three doses of injection that must be given within a one year period. Any person in the age group of 9 to 26 can receive the first dose. The second dose is typically given two months after the first, and the final dose is given six months after the first (Drug Information Online; Net Doctor).
Clinical researchers have discovered that giving three doses of Gardasil allow women’s antibody levels against those HPV strains to progressively increase with each dose. They believe this may provide women with greater immunity for a longer duration than could be provided with only one dose (Gostout). However, since some studies have been finding that higher antibody levels do not correlate with greater immunity from HPV infection, this three dosage schedule may be changed in the future (McCormack and Joura).
How Gardasil Works
There are different types of vaccines, including inactivated; live, attenuated; toxoid; conjugate; subunit; DNA; and recombinant vector vaccines (U.S. Department of Health and Human Services of National Institutes of Health).
Adapted from Minestrone Soup/Wikimedia CommonsFigure 2 (Click here to view enlarged image.): Gardasil is a recombinant vaccine made by taking capsid-encoding genes from HPV types 6, 11, 16, and 18 and expressing them in yeast cells. The proteins made by the yeast cells are purified and used in the vaccination. Since the vaccine contains only HPV proteins and not the entire virus, it does not cause infection and allows the body to develop acquired immunity to those specific HPV strains.
Gardasil is a type of recombinant vaccine, as shown in Figure 2. The Gardasil recombinant vaccines are made by taking genes that encode for capsid proteins of HPV types 6, 11, 16, and 18 and inserting them into yeast expression vectors, which are circular DNA pieces containing specific sequences that allow translation of those genes into proteins. The HPV protein-encoding genes are expressed in the yeast vectors to create large amounts of protein, which are then purified and used in the vaccine (McCormack and Joura; U.S. Food and Drug Administration, “Gardasil”).