HPV vaccines have been studied for a long time and have been shown to be safe and effective in preventing infection with the types of HPV that are most associated with cancer and genital warts. Vaccines have been in use for at least 15 years, and clinical trials have already demonstrated safety and efficacy. [1]
Studies have shown that HPV vaccines are very effective in preventing infection with the types of HPV included in the vaccine. Vaccines have been shown to provide protection against the development of cervical, oropharyngeal, penis, vaginal and vulvar cancers, as well as genital warts. Vaccines are most effective when administered before exposure to HPV, which is why vaccination is recommended for girls and boys before they become sexually active [2].
The nonavalent vaccine is designed to protect against HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58. The vaccine's efficacy in preventing infections and diseases associated with these types has been demonstrated in clinical trials. It showed nearly 97% efficacy in preventing cervical, vulvar, and vaginal cancers caused by the five additional high-risk HPV types (31, 33, 45, 52, 58) that were not covered by the original quadrivalent vaccine. It continued to demonstrate almost 100% efficacy against diseases caused by HPV types 6, 11, 16, and 18, which were already covered by the original vaccine [3].
While the exact duration of protection of Gardasil 9 is not yet fully known, studies indicate that it provides sustained protection. The antibodies produced in response to the vaccine remained at levels expected to provide protection for at least six years after the initial vaccination, and the duration is likely much longer based on ongoing studies [4].
HPV vaccines have an excellent safety profile. Vaccines have been widely tested in clinical trials involving thousands of participants. The most common side effects are mild and include pain, redness, or swelling at the injection site, and occasionally fever, headache, or muscle pain. Serious side effects are rare and have not been directly related to the HPV vaccine. The benefits of vaccination far outweigh the risks, and the HPV vaccine is safe for most people [4].
In clinical trials involving tens of thousands of participants, the nonavalent vaccine demonstrated a safety profile consistent with that of the quadrivalent vaccine, which had been extensively studied and was in use for several years prior to the introduction of Gardasil 9.
The most common side effects of the Gardasil 9 vaccine are similar to other vaccines and include injection site reactions (pain, swelling, and redness at the injection site are common but generally mild and short-lived) and general side effects, which might include fatigue, headache, fever, and nausea.
HPV vaccines are not effective against all types of HPV and vaccines do not provide protection against HPV infections that a person may already have. Therefore, it is still important that people who have been vaccinated continue to have a responsible sex life and regularly participate in screening for cervical cancer [5].
In countries where high vaccination rates are recorded, there are also real-world data on the impact of vaccination: reducing infections, and preventing precancerous cervical lesions and genital warts, both in men and women. For example, Australia, which has been a frontrunner in HPV vaccination, saw a significant decrease in the prevalence of vaccine-related HPV types among young women. Within a decade of the vaccine's introduction, infections with HPV types 16 and 18 (the types responsible for the majority of cervical cancers) decreased by over 80% among women aged 18-24. Also, there was a 90% reduction in genital warts among young women aged less than 21 years within eight years of the vaccine's introduction [6]. In Scotland, within a decade of introducing the vaccine, there was an 89% reduction in CIN3+ (a high-grade cervical abnormality) in women who were vaccinated at age 12-13 [6].
Countries with high HPV vaccination rates have also seen reductions in HPV infections among unvaccinated individuals, suggesting the presence of herd immunity. This was observed in both Australia and the U.S., where declines in HPV prevalence were noted not only among vaccinated individuals but also among those who had not been vaccinated [7]. These real-world outcomes reaffirm the importance and effectiveness of HPV vaccination programs. By providing evidence of the vaccine's impact beyond clinical trials, these findings underscore the vaccine's role in reducing the burden of HPV-associated diseases on a population level. As HPV vaccination programs continue and coverage rates increase, further reductions in HPV-related diseases are anticipated worldwide.
Ongoing post-marketing surveillance in various countries has consistently found the safety profile of HPV vaccines in real-world settings to align with clinical trial data. The vast majority of reported side effects are non-serious.
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