Paper I
2025 March (Supplementary (SAY)) (2019 Scheme) · 100 marks · 180 min

Question

Human papilloma virus and the role of vaccines

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Answer

Human papillomavirus (HPV): a small, non-enveloped, double-stranded DNA virus, with over 100 genotypes identified; classified into low-risk types (e.g., HPV 6, 11 — associated with genital warts/condyloma acuminata) and high-risk (oncogenic) types (e.g., HPV 16 and 18, the most important, together responsible for the majority of HPV-associated cancers). HPV infection is the necessary cause of virtually all cervical carcinoma, and is also implicated in a proportion of anal, vulvar, vaginal, penile, and oropharyngeal cancers. Oncogenesis is driven by viral E6 and E7 oncoproteins, which inactivate host tumour-suppressor proteins p53 and retinoblastoma protein (Rb) respectively, promoting uncontrolled cell proliferation.

Role of vaccines:

  • HPV vaccines are prophylactic, based on virus-like particles (VLPs) of the major capsid protein L1, which induce a strong neutralizing antibody response without containing any viral genetic material (non-infectious).
  • Available formulations include bivalent (types 16, 18), quadrivalent (types 6, 11, 16, 18), and nonavalent (covering 9 types, including additional high-risk types) vaccines.
  • Administered ideally to adolescent girls (and increasingly boys) before the onset of sexual activity/HPV exposure, for maximal effectiveness, typically as a 2-dose (age <15 years) or 3-dose (older age/immunocompromised) schedule.
  • Effectiveness: demonstrated to significantly reduce the incidence of HPV infection, genital warts, cervical intraepithelial neoplasia (precancerous lesions), and, with long-term follow-up, invasive cervical cancer itself.
  • Vaccination is a key component of cervical cancer prevention strategy, complementing (not replacing) regular cervical cancer screening (Pap smear/HPV DNA testing), since the vaccine does not cover all oncogenic HPV types and offers no therapeutic benefit against pre-existing infection.

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