of such cancers caused by HPV, but this has not been demonstrated. In June 2020, the FDA approved the use of Gardasil for the prevention of head and neck cancers. The FDA approved Gardasil 9 for women and men aged 27 to 45 based on the vaccine being 88% effective against persistent HPV infections that cause certain types genital warts and cancers in females. Vaccine efficacy in males in this age group was inferred. Efficacy A 2020 longitudinal study tracking over 1.6 million Swedish girls and women over an eleven-year period found half as many cervical cancer cases in all women who had been vaccinated, and amongst women who had been vaccinated before the age of 17 a 78% reduction in cervical cancer, "a substantially reduced risk of invasive cervical cancer at the population level." An alternative vaccine known as Cervarix protects against two oncogenic strains of HPV, 16 and 18. The National Cancer Institute says, "To date, protection against the targeted HPV types has been found to last for at least 10 years with Gardasil, at least 9 years with Cervarix, and at least 6 years with Gardasil 9. Long-term studies of vaccine efficacy that are still in progress will help scientists better understand the total duration of protection." Gardasil has been shown to be partially effective (approximately 38%) in preventing cervical cancer caused by ten other high-risk HPV types. Antibody levels at month 3 (one month post-dose number two) are substantially higher than at month 24 (18 months post-dose number three), suggesting that protection is achieved by month 3 and perhaps earlier. In 2014, the World Health Organization (WHO) recommended that countries offer the vaccine in a two dose schedule to girls aged under 15, with each dose at least six months apart. The United Kingdom, Switzerland, Mexico, and Quebec province of Canada are among the countries or territories that have implemented this . The CDC recommended the vaccines be delivered in two shots over six months. Males Gardasil is also effective in males, providing protection against genital warts, anal warts, anal cancer, and some potentially precancerous lesions caused by some HPV types. Gardasil vaccine has been shown to decrease the risk of young men contracting genital warts. In the United States, the FDA approved administration of the Gardasil vaccine to males between ages 9 and 26 in 2009. The FDA approved administration of the Gardasil 9 vaccine