HPV vaccine to protect against cervical cancer
Human papillomavirus (HPV) infections play a critical role in the development of cervical cancer. There is now a vaccine against these sexually transmitted viruses. It targets the most common of the carcinogenic (cancer-causing) HPV viruses, but does not provide complete protection against cancer.
Over the past few decades the number of women with cervical cancer has decreased drastically in some countries, including Germany. This kind of cancer is still a life-threatening disease, though. Specific forms of human papillomavirus (HPV) infections are considered to be the main cause of cervical cancer. HPV infections occur in humans only, affecting skin and mucous membrane cells. They can be spread through direct contact with infected skin or mucous membranes. HPV infections usually go unnoticed, do not cause any symptoms and clear up on their own.
More than 100 different strains of HPV are currently known. Some cause warts to grow on the skin (also called papillomas). About 40 different HPV strains can infect skin and mucous membranes, especially in the genital area. The viruses are transmitted sexually, but they are spread through contact with skin and mucous membranes, and not through bodily fluids.
Because these HPV viruses are very common, it is estimated that as many as 90% of all sexually active women and girls become infected.
What are the consequences of an HPV infection?
The body’s immune system usually destroys the viruses relatively quickly on its own, without any health consequences. An infection typically lasts about eight months. If the infection is not successfully fought off and the virus stays in the cells of the skin or mucous membranes, the affected tissue may start to change over time. In women, this most commonly occurs around the cervix, but it can also occur in the mucous membranes lining the vagina, although this is extremely rare. These kinds of changes are called “dysplasia.” There are three levels of severity: “low-grade dysplasia,” “moderate dysplasia” and “high-grade dysplasia.” Doctors often refer to these as “CIN” grades (CIN 1 to CIN 3).
Cervical cancer only tends to develop in women who have been infected with certain virus strains. Two strains of the virus, known as HPV 16 and 18, are considered to be high-risk strains: It is estimated that they are involved in the development of 70% of all cases of cervical cancer worldwide. Infections with these cancer-causing HPV viruses have been recognized as a cause of cervical cancer since the 1980s.
Infections with some other strains of HPV viruses can lead to irritating but harmless warts (condylomas) in the genital area. Many of these warts cannot be seen or felt, but some form hard nodules with an uneven surface. 90% of these warts are caused by the HPV strains 6 and 11. On average, about 1% of the population have genital warts, but they are more common in sexually active young people. The warts disappear on their own without treatment in 20% - 30% of all people who have them.
What does the HPV vaccine protect against?
A vaccine (trade name: "Gardasil" or “Silgard") that provides protection against the HPV strains 16 and 18, as well as 6 and 11, has been available since 2006. The strains 6 and 11 are not considered to cause cancer, but they can cause genital warts. A second approved vaccine (trade name: "Cervarix") only targets the strains 16 and 18. It does not offer protection against genital warts.
No published scientific studies have directly compared the two vaccines to see how well they prevent abnormal cell changes (dysplasia) in women and girls. A vaccination will not have any effect on pre-existing HPV infections or genital warts.
Who is the vaccine intended for?
In August 2014 the German Standing Committee on Vaccination (STIKO) issued a recommendation that all girls between the ages of 9 and 14 be given an HPV vaccine. These costs are covered by German statutory health insurers. Anyone who is unvaccinated needs to have the vaccination before the age of 17 at the latest. Some insurers also cover the costs of vaccination beyond the age of 17. The question of whether boys could or should also be vaccinated is still being considered.
In order to prevent young women from becoming infected with HPV early on, it is recommended that they be vaccinated before they become sexually active, if possible. But it is not exactly clear at what age it is best to have the vaccine. Most of the studies that looked at how effectively HPV vaccines prevent abnormal cell changes involved women and girls over the age of 15.
What does the vaccination involve?
The vaccine is injected into the muscles of the upper arm. The vaccine does not contain viruses able to reproduce inside the body. It is made up of proteins that are like the outer coat of HPV viruses. It is not possible for the vaccine to cause an infection, but it does trigger a response from the body's immune system, and protective antibodies are produced.
Depending on the woman's age when she receives the first shot, a total of two or three shots are needed for full protection.
How well does the HPV vaccine work?
Randomized controlled trials have shown that that the vaccines prevent moderate and high-grade dysplasia caused by the HPV strains 16 and 18.
The largest study, involving over 17,000 women and girls, produced the following results:
- Without the vaccine: 2 out of 100 unvaccinated participants developed high-grade dysplasia (CIN 3) within four years.
- With the vaccine: 1 out of 100 vaccinated participants developed high-grade dysplasia (CIN 3) within four years.
In other words, the vaccine prevented the development of high-grade dysplasia in 1 out of 100 women and girls.
These women have a noticeable benefit from the vaccine because it means they do not have to have surgery: there is a chance that high-grade dysplasia can turn into cervical cancer. For this reason doctors usually recommend having this kind of abnormal tissue surgically removed.
The vaccine against four virus strains was also shown to have another effect: Participants who had the vaccine developed fewer genital warts, as two studies involving 6,000 women and girls found. 4 out of 100 participants who did not have the vaccine developed genital warts, compared to just 1 out of 100 participants who did have the vaccine.
Some questions were left unanswered by the studies: Not all of the participants had all three vaccination shots. The results might have been better if they had been fully immunized. It is also not clear how long the protection lasts, because most of the participants were only followed up over a period of up to four years. But it usually takes several years to several decades for cervical cancer to develop.
What side effects does the HPV vaccine have?
The studies did not show any serious side effects, at least within the four-year duration of the studies. The possible long-term side effects of the vaccine are not yet known.
According to the U.S. health agency CDC, the vaccine may lead to various reactions at the site of injection, including pain (80 out of 100 vaccinations), skin redness (20 out of 100 vaccinations), and tissue swelling (3 out of 100 vaccinations). Problems such as indigestion, headaches, tiredness or muscle pain may also occur, but are less common.
The U.S. regulatory agency FDA warns that there is a general risk of teenagers fainting after being given a shot. This means that it is important to stay at the doctor's for about 15 minutes after having an HPV vaccine.
Can the vaccine protect against cervical cancer?
The HPV vaccine prevents infection with certain HPV strains that may cause cancer. It can also reduce the number of cases of high-grade dysplasia (CIN 3). This suggests that the HPV vaccine could also provide long-term protection against cervical cancer. But because cervical cancer usually develops over several years or decades, it will still take some time before we know for sure. The studies only observed the women and girls for less than four years after they had the vaccination.
Another way of preventing cervical cancer is to have regular smear tests (Pap tests) for the early detection of cervical cancer. This can detect most abnormal cell changes, making it possible to get early treatment.
In general, it is good for young women to know about how they can protect themselves against sexually transmitted diseases. This is not only true for HPV.
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