HPV vaccination protects even unvaccinated women, says Swedish study: AIIMS doctor on why this holds a big lesson for India

What the study found

The study from Sweden looked for pre-cancerous lesions in unvaccinated women across four cohorts born between 1989 and 2000. The 1989-92 cohort received subsidised vaccination, reaching a coverage of 25% and the 1993-98 cohort was eligible for catch-up vaccination, reaching a coverage of 55%. The 1999-2000 cohort participated in a school-based vaccination programme, reaching a coverage of 80%.

The study found that with a high vaccination coverage in the 1999-2000 cohort, pre-cancerous lesions went down in even the unvaccinated women. Such women born in 1999 and 2000 in Sweden, who grew up alongside peers vaccinated through a school-based programme, had about half the risk of developing serious precancerous changes in the cervix compared with unvaccinated women born between 1985 and 1988, when vaccination uptake was lower and only given to women who sought it.

The study found the incidence to be 1.17 in the first cohort, 1.06 in the second cohort, and 0.54 in the third cohort per 1,000 person years. “This provides a real-world evaluation of herd effect,” researchers said.

Dr Neerja Bhatla, professor and head, Obstetrics and Gynaecology, says, “While there is no data on herd immunity from India because we haven’t had enough HPV vaccination yet, we have known about the herd effect. Australia has previously shown that after it launched its HPV vaccination campaign, genital warts went down in not just women but also men. In the UK, when researchers looked at pre-cancerous lesions in the cohort that had received vaccines, they found that it had almost been eliminated.”

What are lessons for India?

With India planning to vaccinate girls between the ages of nine and 14 years through similar school-based programmes — followed by the vaccine being included in routine immunisation — the indications may start showing up a few years later. “It will depend on what we are looking for. Genital warts are the first indication that the number of HPV infections is reducing. It will take a while to see a reduction in cancer incidence,” says Dr Bhatla. The vaccine is most effective when it is administered in this age group, with reducing efficacy as the girls grow older. “The aim should be to achieve a high vaccination coverage so that the others in the population are also protected. A coverage of 90% among the girls is desirable, but we need a coverage of at least 70%,” she adds.

Better mapping of risks

Not only will it reduce cancer incidence in time, a happy side-effect would be the requirement for fewer triage testing. “When someone is found to be positive through pap smear, HPV test or visual inspection with acetic acid, it only tells us who is at risk of developing cervical cancer. You would need biopsy and CIN test to confirm cancer. The requirement for all of these tests will reduce as HPV incidence goes down,” says Dr Bhatla.

More than 95% of all cervical cancer cases are linked to persistent infection with certain high-risk strains of HPV. At least 14 HPV types have been identified to have the potential to cause cancer. Among these, HPV types 16 and 18 are considered to be the most oncogenic, causing about 70 per cent of all cervical cancer cases globally.

The quadrivalent vaccines currently available, including the one manufactured by Serum Institute of India, prevent the entry of HPV 16, 18, 6 and 11, the four of the most common types of HPV. Hence, it has to be administered before women are sexually active. Vaccination prevents infections, genital warts and eventually cancer.

Since HPV infection is also linked to cancers of anus, vagina and oropharynx, there is likely to be a drop in the incidence of these cancers as well.