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Role of HPV vaccines for the prevention of cervical cancer

Cervical cancer is the second most common cancer among Indian women with nearly 1.2 lakh new cases and 70000 deaths every year. However, it is also one of the most preventable cancers in our body. January is observed as a cervical cancer awareness month to raise awareness about the disease and its preventive measures, most importantly the vaccine against Human Papilloma Virus (HPV). 

Cervix cancer is caused by infection by a virus called the Human Papilloma Virus (HPV), which is transmitted through sexual contact. There are many subtypes of this virus, some of which are oncogenic (cancer-causing) high-risk types. Many women are infected by this virus sometime during their reproductive life but the majority (70-90%) of these are asymptomatic and resolve spontaneously. However, when this is not cleared by the body and becomes persistent, it can cause changes in the cervix and lead to precancerous lesions, which if undetected and untreated, may progress to cervical cancer. HPV infection is hence called an “essential” cause of cervical cancer. Additionally, this infection is associated with head and neck (oropharyngeal) and anogenital cancers as well as with anogenital warts and respiratory papillomatosis.

The change from the acquisition of HPV infection to cancer may take 15-20 years or even longer. Among women with persistent HPV infection, the high-risk factors for the development of invasive cancer are immunosuppression (e.g. HIV +ve women or those on immunosuppressant medication), co-infection with other sexually transmitted infections, early age of onset of sexual activity, early age of first pregnancy, multiple pregnancies, multiple sexual partners, tobacco use in any form and hormonal contraceptives.

Preventive vaccines have been developed for the prevention of HPV infection and consequently cervical precancer and cancer. These vaccines do not contain any live biological products or viral DNA and are hence non-infectious and safe. They are either bivalent (effective against HPV 16, 18), quadrivalent (effective against two additional subtypes responsible for causing warts) or nonavalent (aimed against 9 high-risk HPV subtypes). These vaccines are highly immunogenic and protect against HPV infection and cervical precancer in nearly 98-100% of vaccinated girls less than 15 years of age. This efficacy is still good for older girls and women but not as optimum as when the vaccination has been carried out below 15 years of age. They have been shown to impart protection against HPV infection as well as precancerous lesions up to 11.5 years post-vaccination. Besides, these vaccines have been found to be safe and apart from local injection site pain and swelling, are not reported to have any major adverse reactions.

Also Read About the Importance of Vaccination

For best protection against HPV infection, these vaccines are ideally administered before the onset of sexual activity i.e. before exposure to HPV. They are indicated for use in girls from 9-14 years of age. However, as a catch-up approach for girls who did not receive the vaccine at the optimum time, the vaccine can be administered to women up to the age of 26 years. HPV vaccination can be given up to the age of 45 years with prior HPV DNA testing. Two doses of vaccine 5 months apart are recommended for girls between 9 & 14 years of age, while from age 15, a 3-dose schedule is recommended. Studies are underway to test the efficacy of a single dose of vaccine, results of which are awaited. One of the obstacles to the wide use of this vaccine in India has been the cost and consequent inability to reach the economically lower strata of society, especially in the rural areas. With the scientifically tested Indian HPV vaccine now on the horizon, with a predicted lower cost, we should be able to cover the majority of eligible girls and women to vaccinate them.  

It is important to understand that this vaccine is against HPV infection and not cervical cancer. Since the presently available HPV vaccines do not protect against all known high-risk oncogenic HPV subtypes, it is essential that women continue to get themselves screened appropriately with pap smears and HPV DNA testing to achieve complete protection against cervical cancer.

The high burden of cervical cancer & the high efficacy and safety of HPV vaccination justify its introduction in the Indian National Immunization Programme to substantially reduce the cervical cancer burden in the future.