How effective is HPV vaccination in preventing cancer?

Q & A with Dr. Rani Bhat

How effective is HPV vaccination in preventing cancer?

The human papillomavirus or HPV is the name given to a group of related viruses. There are more than a hundred types of HPVs and about forty of them are transmitted sexually. These viruses are generally divided into two groups known as low and high-risk types. The low-risk virus can cause genital warts and high-risk type causes various cancers of the reproductive organs, like cervical, vaginal, penile, vulvar, and anal and oropharyngeal cancers. Of the high-risk HPV, types 16 and 18 are responsible for about 70% cases of cervical cancers globally.

What is HPV vaccination?

Human papillomavirus (HPV) is a sexually transmitted virus that causes anogenital and oropharyngeal cancer in males and females.

Vaccines have been developed to protect against acquiring HPV infection. There are three types of vaccination, which vary in the number of HPV types they contain and not all are available in all countries:

• Quadrivalent (Gardasil) HPV vaccine: this targets HPV types 6, 11, 16,18
• 9-valent (Gardasil 9) vaccine: this vaccine targets the same HPV types of virus such as the quadrivalent vaccine (6, 11, 16, and 18) as well as types 31, 33, 45, 52, and 58
• Bivalent (Cervarix) vaccine: this vaccine targets only HPV types 16 and 18

Rationale for HPV vaccination in -

Females

These vaccines provide direct protection to female recipients against HPV infection and keep at bay cancers caused due to the virus. This preventive outcome is most beneficial against cervical cancer, the most common cancer in females worldwide. HPVs 16 and 18, which are covered by all three available vaccines (9-valent, quadrivalent, or bivalent HPV vaccine) and are responsible for 70% of all cervical cancers. HPV types 31, 33, 45, 52, and 58, which are targeted by the 9-valent vaccine, cause an additional 20 percent of cervical cancer cases.

HPVs 16 and 18 are also responsible for almost 90% of all anal cancers and a significant proportion of vaginal, oropharyngeal and vulvar cancers. Quadrivalent and 9-valent vaccines also prevent anogenital (anus and nearby genital areas) warts. About 90% of anogenital warts are caused by HPVs 6 and 11. Although these warts are merely lesions on the external genitalia, they cause psychological and physical morbidity. Anogenital warts are also very difficult to treat.

Males

Anal cancer afflicts both men and women. HPV vaccination also protects males against this form of cancer that can result from chronic HPV infection. As has been noted above, HPVs 16 an 18 are responsible for almost 90% of all anal cancers and a considerable proportion of penile and oropharyngeal cancers. Since quadrivalent and 9-valent vaccines also target HPV types 16 and 11, which we have seen, are responsible for 90% of all anogenital warts, it is clear that vaccination even protects males from this morbidity.

Incidentally, men are less vulnerable to HPV-associated pre-cancers and cancers than women are to cervical cancer. Despite an overall lower direct benefit of HPV vaccination in males as compared to females, the actual advantages of male vaccination outweigh the lower risk factor by population benefits from the herd immunity.

How do vaccines protect against HPV infection?

The vaccines, particularly Gardasil 9, are composed of microscopic proteins that resemble the exterior of the actual humanpapilloma virus. The vaccines also contain immune-boosting substances like sodium chloride or salt, aluminium, water molecules, L-histidine, borax, and polysorbate 80. These substances also maintain stability in the chemical composition of the vaccine but also make it suitable for human injection. The vaccines do not include the actual virus or even its DNA.

After the vaccines are injected, the immune system responds by making antibodies to the proteins that look like the actual HPV, so they know what to attack and kill when HPV infection actually takes place. When the person is exposed to the real HPV, the antibodies kill it and prevent the virus from entering the cells.

Who is eligible for HPV vaccination?

Despite their universal benefits, not everyone is medically fit for HPV vaccination. The Advisory Committee on Immunization Practices (ACIP) of the United States recommends general HPV vaccination between these ages in females as well in males:

• Routine HPV vaccination is recommended to all children from 11 or 12 years of age and can be vaccinated though the minimum age of nine years.
• Adolescents and young adults who have either not been previously vaccinated or have not completed the vaccination doses begun in the earlier age group are advised to get vaccinated or complete the series between the ages of 13 and 26 years of age.
• Catch-up vaccination is not generally recommended for adults aged 27 years and older; the ACIP is of the opinion that people after the age of 27 should be vaccinated only if the case demands it.
• The possibility of exposure to HPV increases as we age. Hence, the cost-effectiveness and herd immunity benefit is lower in people over 27. However, for some people, like those who have not had sex or have a limited number of prior sexual partners, the chances of prior HPV infection could be very low. Such people could be eligible for vaccination.

Though these recommendations are consistent with those of other prestigious medical groups in the United States, Europe, and the World Health Organization, they may not be applicable to people in other parts of the world. Since eligibility depends on sexual behavior the recommendations could be tailor-made for people in countries with conservative sexual attitudes.

The optimal time frame for HPV immunization within the prescribed age-range is before an individual has sex for the first time. Clinical trials of HPV vaccine effectiveness in both females and males reveal that HPV immunization is most efficacious in individuals who have not been exposed to HPV infection. Remember, these vaccines are not formulated to treat pre-existing infections.

Sexually active individuals can still be vaccinated if they fall under the recommended age groups. History of genital warts, or abnormal PAP smear or any other HPV infection should not be a contraindication to HPV vaccination. However, it should be reiterated that HPV immunization has lower benefits for individuals who have already been infected with one or more of the HPV types.

People who are indirectly not eligible for HPV vaccination

Even though you may be in the right age groups, you should not get vaccination if:

• you have a yeast allergy
• you are pregnant. However, research suggests no significant hazard on you or the baby if you are vaccinated and later become pregnant
• you have a bleeding disorder, though you may be eligible if your doctor thinks so
• people with anaphylaxis of serious allergy to a previous vaccine or to any of the ingredients that go in its formulation

Parents should mention to their doctors about the effects of any previous vaccination or medicines in their children.

How effective are HPV vaccines?

Gardasil 9 is shown to be highly effective. This vaccine provide near-100% protection from nine types of HPV, namely types 6, 11, 16,18,31,33,45,52, and 58. But this is only when all scheduled doses are received at the right intervals, and when vaccination is given before any HPV exposure.

Individuals aged 14 or younger at the time of their first immunization need two vaccine doses at least six months apart.

Individuals over 15 years need three doses of the vaccine over a period of six months. This is because it has been noted that younger the age they have the tendency to produce the best immune response to the vaccination, hence older kids need three doses.

In 2003 clinical trials, it has been shown that the vaccines still provides close to 100% protection more than a decade after it was first injected. And the effect does not show any signs of weakening over the period of time. Ongoing research has already proven to be successful in reducing the rates of HPV infections, pre-cancer of the cervix and genital warts.

Are there any side effects?

The side effects of HPV vaccines in people are similar to what they experience after other vaccines. The most common side effects of any vaccination are

• pain
• swelling or redness at the injection site

Though these reactions occur in four out of five people, they are temporary, which also proves how fast the immune system responds to the vaccine. The reactions themselves be treated with a cold pack or a dose of paracetamol if required.

Though there can be a more serious side effect like allergy, it is an extreme rarity. There are only cases of allergy in more than one million vaccinations. This rate is similar to other vaccines given to babies and children. Allergic symptoms show up pretty fast, usually within 10 minutes of vaccination. It commonly happens if you are naturally allergic to any ingredient in the vaccine, like yeast.

Children are usually monitored for 15 minutes after the injection to ensure they do not produce an allergic response. If an allergy occurs, it can be successfully treated.

Claims of Premature Menopause as a Side Effect

Concerns were raised recently about the quadrivalent HPV vaccine causing a very rare condition of premature menopause also known as Primary Ovarian Insufficiency (POI) and Premature Ovarian Failure (POF).

The claims were circulated on media and were based on six cases reported since 2007 when HPV vaccination programs were accelerated in some western countries. However, the fact is that over 200 million injections of the quadrivalent HPV vaccine were administered all over the world. There is no scientific, medical or epidemiological evidence to suggest that the vaccine could have been responsible for the premature menopause.

The World Health Organization, the Centers for Disease Control and Prevention of the USA, and the Australian Advisory Group on Immunization, and many other expert medical groups continue to advocate the implementation of the HPV immunization programs to prevent diseases caused by the human papilloma virus.

Thus, it is of paramount importance that parents and individuals get their information from credible sources and consult the best medical practitioners.

Do women who have already been vaccinated need to be screened for cervical cancer?

There are more than a hundred HPV types and the vaccines that we have at present can protect against only nine virus types and may give cross cover to other types of viruses. The other types may also be responsible for cancer-causing infections. Hence, HPV vaccination today cannot be a substitute for regular cervical cancer screening. Screening helps doctors detect pre-cancerous conditions in the cells of the cervix. However, screening becomes a necessity for women who have not been HPV immunized.

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