This week’s column discusses the World Health Organization’s (WHO) first pillar in its global strategy for Cervical Cancer elimination – 90 per cent of girls should be vaccinated by age 15. As mentioned in last week’s column, the Human Papilloma Virus (HPV) is the main cause of Cervical Cancer. By age 25, 90 per cent of sexually active people would have been exposed to the HPV, making it the most common sexually transmitted infection. Most (90 per cent) HPV types do not cause any signs or symptoms; our body’s immune response resolves them. However, in some cases, HPV infection persists, resulting in either genital warts or precancerous lesions (abnormal changes of cells), which, if undetected, can progress to cancer. While they are more than 100 strains of HPV, 13 strains are considered high risk i.e. they can potentially cause cancer. Together, they are responsible for all cervical cancer cases. Of these, strains 16 and 18 are the most aggressive, accounting for at least 70 per cent of cervical cancers.
HPV ASSOCIATED CANCERS
HPV infects both women and men and has been responsible for most anal and oropharyngeal (mouth, throat) cancers. In females, it is linked to vaginal and vulvar cancers, and in males, penile cancer. The burden of HPV-related diseases in the world is significant. In 2018, 690,000 cases of cancers were attributable to high risk HPV. The highest was related to the cervix with 570,000 cases globally (almost 83 per cent) and the remaining were linked to anogenital and oropharyngeal cancers, with more than 90 per cent occurring in lower-middle income countries.
WHY IS THE VACCINE RECOMMENDED BY AGE 15? CAN THE VACCINES BE GIVEN AFTER?
The vaccines do not treat pre-existing HPV infection or HPV associated disease. Therefore, vaccination is recommended prior to initiation of sexual activity. The Advisory Committee on Immunisation Practices (ACIP) recommends that the vaccines can be extended to age 26 in women and age 21 in men, if not vaccinated previously. In special populations that are of a higher risk of developing HPV-related cancers, such as men who have sex with men and immune-compromised persons (including HIV infected persons), and those who may not have been vaccinated previously or may not have received all the doses, the vaccines can also be extended to age 26.
Three types of HPV vaccines have been developed, targeting several types of HPV: Cervacix – targets HPV strains six and 11 (responsible for genital warts); Gardasil – targets HPV strains six, 11, 16 and 18 and Gardasil 9– targets the strains mentioned above and five others.
From a public health perspective, evidence suggests the HPV vaccines offer comparable immunogenicity, efficacy and effectiveness in preventing cervical cancer. In Guyana, we use the Gardasil vaccine. These vaccines have shown 90-100 per cent effectiveness against HPV types 16 and 18 and have also demonstrated “cross protection” against non-targeted high-risk types of HPV. In other words, they offer protection to other strains of HPV as well.
VACCINE DOSING AND INTERVAL
All three vaccines are administered in either a two or three-dose schedule which varies depending on age, HIV and immune status. The WHO recommends a minimum interval of six months and a suggested maximum of 12-15 months. However, this interval can be extended in cases of vaccine shortages. Interestingly, data from vaccination registries have shown protection in persons who did not receive the full three-dose; thus, benefits are noted with one or two doses of the vaccines. However, the maximum effect is achieved if all doses are completed.
BENEFITS OF THE VACCINES
Evidence of the benefits in those who received the vaccines, i.e., the decline in HPV infection rates, genital warts and precancerous lesions and cancer, were observed in several countries. By 2015, Australia observed reduced cervical HPV infection rates in women aged 18-24 years after vaccination with Gardasil, from 92 to 1.5 per cent and a 92.6 per cent decline in genital warts in females less than 21 years. Sweden recorded an 88 per cent and 53 per cent reduction in invasive Cervical Cancer rates in girls who were vaccinated before age 17 and at age 17 and above respectively.
Additional benefits including strong “herd immunity” effects have also been observed. “Herd immunity” is the effect observed when approximately 70 to 80 per cent of a population is vaccinated, thus reducing the virus’ spread among the unvaccinated population. An example of this effect was observed in Australia in unvaccinated boys less than 21 years who displayed an 81.8 per cent decline in genital warts.
Given all the benefits of the vaccines, achieving this WHO pillar becomes crucial. Accomplishing this 90 per cent vaccination target by age 15 would require advocacy and information on the disease and the benefits of the vaccines; programme funding; establishing and maintaining public trust in the vaccines; and strong collaboration between the Ministries of Health and Education (most girls at age 15 will be in school).
This target is achievable – Australia has successfully implemented the world’s first and largest HPV immunisation programme. We can look to these countries and learn from them. I reiterate the call for all of us to play our part in eliminating this disease. We will not only be saving lives but will also reduce suffering and the need for costly medical interventions while improving the quality of life of women in Guyana.