HPV vaccination: effective cancer prevention

The majority of sexually active men and women are infected with the human papillomavirus. HPV - or HPV for short - is responsible for the development of various types of cancer, especially cervical cancer. Vaccination provides protection.

What is the human papillomavirus?

The human papillomavirus, medically known as the human papillomavirus and commonly abbreviated as HPV, belongs to a group of nonenveloped DNA viruses (the Papillomaviridae family). These viruses are highly specialized: they infect only human cells, particularly what are known as epithelial cells. This refers to the outermost layer of cells in the skin and the mucous membranes of the genital area or the oropharyngeal region.

The Mechanism of HPV Infection

At the molecular level, the virions (the infectious virus particles) enter the body through tiny, often microscopic injuries to the skin or mucous membranes (microtraumas). They migrate to the lowest layer of the epidermis, known as the basal layer. There, the virus inserts its genetic material (genome) into the nucleus of the human host cell.

Since the human papillomavirus—like all viruses—has no metabolism of its own, it acts as a cellular parasite: it “hijacks” the human cell’s machinery to replicate its own genetic material millions of times and release new viral particles.

The strategy of immune evasion: A distinctive feature of HP viruses is their ability to evade the immune system. The virus is a master of camouflage and skillfully evades detection by the immune system. Since the virus replicates exclusively in the upper layers of the skin, which are not directly connected to the bloodstream, the immune cells often do not receive the warning signals.

This is the main reason why a natural infection usually does not elicit a strong enough immune response to provide lasting protection. In contrast, the HPV vaccine triggers a much stronger and more targeted production of antibodies in the blood, which can neutralize the virus on the surface as soon as it comes into contact with the body.

Classification of HPV Types

To date, scientists have identified more than 200 different HPV genotypes. For medical screening, the most important factor is the classification into two clinical groups, which differ in their potential to cause malignant tissue changes:

• Low-risk HPV types: The most clinically significant types are HPV 6 and 11. These virus types are generally benign and do not lead to malignant tumors. However, they are the main cause of highly infectious genital warts (condylomas). Note: While common skin warts on the hands or feet are also caused by HPV, they are usually caused by genotypes other than those that affect the genital area.
• High-risk HPV types: This group includes about 14 oncogenic (cancer-causing) types, with HPV 16 and HPV 18 accounting for about 70% of all cases of cervical cancer worldwide. These viruses have the ability to produce certain viral proteins (E6 and E7) that disable the body’s own tumor suppression mechanisms. If the viral genetic material integrates permanently into the human host cell and the infection persists for years (persistence), this can disrupt cell division and lead to the development of carcinomas.

Virus Spread and Transmission Risks

The human papillomavirus is one of the most widespread sexually transmitted pathogens in the world. The epidemiological significance is high: Estimates suggest that approximately 70 to 80 percent of the sexually active population will contract at least one infection with one or more HPV types during their lifetime.

Characteristics of virus transmission: Unlike many other sexually transmitted infections, the virus is not primarily transmitted through bodily fluids such as blood or semen. Instead, HPV is transmitted through direct skin-to-mucous membrane contact (or mucous membrane-to-mucous membrane contact). This means:

• Infection can occur even through close physical contact (petting), even without full sexual intercourse.
• While condoms significantly reduce the risk of infection, they do not provide complete protection, as the virus can also colonize areas of the genital region that are not covered by the condom.

From Infection to Disease: The good news is that, thanks to a healthy immune system, most viral infections resolve without symptoms within 12 to 24 months (spontaneous resolution). The risk of serious complications arises only when the immune system is unable to eliminate the pathogen. This so-called persistent (long-term) infection with high-risk types leads to chronic cellular changes over the course of years. If these go undetected, they can develop into malignant tumors, including cervical, vulvar, labial, anal, oropharyngeal, and penile cancers.

Why the HP Virus Is Dangerous for Men, Too

The latter in particular shows that HPV is not exclusively a “women’s issue”, as is commonly assumed. And yet, while most women are familiar with the term HPV after their first visit to the gynecologist at the latest, the majority of men are not aware of the problem. This is incorrect, as Cristian Bronz, a senior physician in the Department of Gynecology, explains: “Although men are less likely to develop severe forms of HPV-related genital cancer, they are fundamentally just as affected as women—and, not least, they are the direct carriers of the virus.”

Because this rarely develops clearly perceptible symptoms, it is usually passed on unconsciously. This is mainly via the mucous membranes during vaginal, oral and anal intercourse. Since the highly contagious HP virus can be transmitted even through petting, it is also dangerous for young, sexually inexperienced women and men. “The risk of infection increases as the number of sexual partners rises.” “That is why the 16–25 age group is currently the most affected by the HP virus,” said Cristian Bronz.

Detecting Precancerous Conditions Caused by HPV and Preventing Them Through Vaccination

HPV itself is not curable. In the vast majority of cases (+/-70 percent), however, the virus disappears again within a year of infection, and in 90 percent of cases within two years. Despite all this, according to the Federal Office of Public Health, more than 5,000 women in Switzerland are diagnosed each year with precancerous lesions of the cervix caused by HPV. During the same period, approximately 200–250 women die from cervical cancer. Cervical cancer is the fifth most common type of cancer in women aged between 20 and 49. This makes early detection all the more important. “The fact that, relative to the overall spread of the virus, we actually have quite few severe cases is precisely due to these preventive measures,” says Cristian Bronz. “Thanks to the early detection of cervical cancer, Switzerland has one of the lowest rates of new cases in the world.”

Prophylaxis is the most important factor in dealing with HP viruses. Strict adherence to safer sex rules, such as the use of a condom or a femidom, reduces the risk of infection, but cannot completely prevent it. Vaccination against HPV is far more effective in this respect. This has been possible in Switzerland since 2006, and the approved vaccines are effective against both tumor-causing HPV types and those that lead to genital warts. “The vaccine triggers an immune response that is far stronger than it would be if one had come into direct contact with the virus,” explains Cristian Bronz. Among other things, the vaccination protects against the seven HP viruses most frequently responsible for the development of cancer.

“Thanks to the early detection of cervical cancer, Switzerland has one of the lowest rates of new cases in the world.”

Ideally, the vaccination should be carried out before sexual contact takes place. The optimal age for HPV vaccination is between the ages of 11 and 15. As the vaccine has only been available for a few years, revaccination is recommended for young adults up to the age of 26. Adolescents up to the age of 15 need two HPV vaccinations every six months, after their 15th birthday they need three. For adults, the probability of benefiting from the vaccination decreases with the number of changing or previous sexual partners, as infection may have already occurred.

Do health insurance companies cover the cost of the HPV vaccine?

As part of the cantonal vaccination programs, vaccination is free of charge for 11- to 26-year-old girls and boys as well as young women and men in accordance with the above recommendations. From the age of 27, health insurance occasionally covers part or all of the costs, which amount to around CHF 800. Health insurance companies and doctors can provide information on this.

Positive Experiences with the HPV Vaccine

At the USZ, the experience with the HPV vaccine has been consistently positive, explains Cristian Bronz; the vaccine used, Gardasil 9, is also characterized by its high tolerability. Vaccinated people would still have lasting protection against the HP virus after ten years. “This suggests a long-term effect,” said Ghisu. “It is not clear at this time whether a booster shot will be necessary at some point.” International studies, for their part, confirm that the vaccine reduces the infection rate for human papillomaviruses as well as for less dangerous warts. In Switzerland, experts believe that 80 to 180 new cases of cancer in men and 300 cases of cancer in women can be prevented every year thanks to the HPV vaccination. “So getting vaccinated definitely makes sense,” Cristian Bronz emphasizes. “You’re not just doing yourself a favor—you’re also doing your partner a favor, and, last but not least, society as a whole.”