HPV vaccine explained

Written by: 
Steve Chaplin, medical writer

This page tackles practical questions about the vaccine. Interested in the debate about HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. immunisation?

Human papillomavirus (HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers.) is a virusA microbe that is only able to multiply within living cells. that infects the skin and the mucous membranesMembranes that line many body structures such as the respiratory tract and the gastrointestinal tract.. More than 100 different types of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. have been identified; these are numbered according to the order in which they were discovered (HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. 1, HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. 2 and so on).

Some types of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. cause the familiar warts of the hands or feet, but about 40 types are sexually acquired and lead to infections of the genitals. Of these, 13 can cause cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. and are classed as high risk; others result in genital warts and are classed as low risk.

Although the infectionInvasion by organisms that may be harmful, for example bacteria or parasites. often clears up without causing symptoms, some types can cause warts on the anusThe external opening of the back passage, the rectum. or genitals

Genital HPV infection

Genital HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. infectionInvasion by organisms that may be harmful, for example bacteria or parasites. is one of the most common sexually transmitted infections. The World Health Organization (WHO) estimates that at any time about 10 per cent of women have cervical HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. infectionInvasion by organisms that may be harmful, for example bacteria or parasites. without any symptoms.

Although the infectionInvasion by organisms that may be harmful, for example bacteria or parasites. often clears up without causing symptoms - 90 per cent of cases disappear without treatment within 2 years - some types can cause warts on the anusThe external opening of the back passage, the rectum. or genitals (anogenital warts), while other types can lead to cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body..

HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. does not cause a strong response in the immune systemThe organs specialised to fight infection.: after an infectionInvasion by organisms that may be harmful, for example bacteria or parasites., only 50-60 per cent of women develop antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. to that particular type of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers., and the level of antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. is relatively low. In addition, there are many different types of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. and infectionInvasion by organisms that may be harmful, for example bacteria or parasites. with one type does not give immunity to the other types. This means that, unlike the case with other common viral infections, a woman may not develop full immunity to HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. and could therefore get further episodes of infectionInvasion by organisms that may be harmful, for example bacteria or parasites..

Infection with two HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. types, 6 and 11, accounts for 90-100 per cent of cases of warts growing on the cervixAny neck-like structure; most commonly refers to the neck of the uterus., vagina, vulva or anusThe external opening of the back passage, the rectum. in women, and on the penis, scrotum or anusThe external opening of the back passage, the rectum. in men. About half of women infected with these HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. types will develop such anogenital warts within 12 months, and 64 per cent will do so within 3 years.

The rate at which anogenital warts are spreading is increasing. They are highly infectious and are most common in 20- to 29-year-olds. They do not cause serious illness (unless transmitted to a child during birth, when they may cause benign tumours throughout the respiratory and digestive tracts in the newborn), but they may well recur, even after treatment.

Statistically, HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. infections that last longer than one year are more likely to lead to cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body., and over 90 per cent of such cancers occur in women. The 13 high-risk HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. virusesMicrobes that are only able to multiply within living cells. cause virtually all cancers of the cervixAny neck-like structure; most commonly refers to the neck of the uterus., about 90 per cent of cancers of the anusThe external opening of the back passage, the rectum., and 40 per cent of cancers of the penis, vagina and vulva. They also cause some cancers affecting the mouth and the head and neck.

Different HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. types cause different cancers, with a similar pattern found throughout the world:

  • The risk of infectionInvasion by organisms that may be harmful, for example bacteria or parasites. is highest soon after a person becomes sexually active; the virusA microbe that is only able to multiply within living cells. can spread by contact, and penetrative sex is not necessary for it to be transmitted
  • 90 per cent of cervical cancers are due to eight common types of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers.: types 16, 18, 45, 31, 33, 52, 58 and 55
  • 70 per cent of cervical cancers are due to just two HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. types: type 16 (54 per cent) and type 18 (16 per cent)
  • HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. also causes abnormalities of the cervixAny neck-like structure; most commonly refers to the neck of the uterus. that, if untreated, may or may not progress to cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. (see Tests and diagnosis).

Cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. is the second most common cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. among women of all ages, and the third leading cause of cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body.-related deaths. The World Health Organization estimates that cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. causes 273,500 deaths worldwide every year.

Cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. is rare among women under 30 and is most frequent among those aged over 45.

Tackling cervical cancer

The main strategies for preventing cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. are:

  • Cervical screening to detect and treat changes to the cervixAny neck-like structure; most commonly refers to the neck of the uterus. that may later develop into cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body.; this is very effective in preventing many cases of cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. in countries with the resources to implement widespread screening programmes. It is more difficult to do this in low- and middle-income countries, where 80 per cent of women with cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. are found
  • Vaccination against HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. for people who are most at risk; the aim is to stimulate their bodies to create antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. against the virusA microbe that is only able to multiply within living cells. and make them immune to the virusA microbe that is only able to multiply within living cells..

Neither strategy provides complete protection.

The vaccines are given as a course of three injections into the muscles of the upper arm over a period of 6 months

HPV vaccines

Two vaccines against the HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. types that cause genital infectionInvasion by organisms that may be harmful, for example bacteria or parasites. are currently available:

  • One protects against infectionInvasion by organisms that may be harmful, for example bacteria or parasites. by HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. 16 and HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. 18, the types that cause 70 per cent of cervical cancers; its brand name is Cervarix
  • The second protects against HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. 16 and 18 and also against HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. 6 and 11, which cause anogenital warts; the brand name of this vaccine is Gardasil.

Both vaccines are given as a course of three injections into the muscles of the upper arm over a period of 6 months.

The vaccines are made from proteins taken from the virusA microbe that is only able to multiply within living cells. itself and reassembled into virusA microbe that is only able to multiply within living cells.-like particles (VLPs) - VLPs do not cause an infectionInvasion by organisms that may be harmful, for example bacteria or parasites., but they stimulate the body's immune systemThe organs specialised to fight infection. to make antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. against the virusA microbe that is only able to multiply within living cells. (that is, they are antigenic). The ability of the immune systemThe organs specialised to fight infection. to recognise HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. antigens is long-lasting, so protection against HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. infectionInvasion by organisms that may be harmful, for example bacteria or parasites. persists for some time (though how long is not currently known).

HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. vaccination produces the best results, in terms of antibodyOne of a group of special proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. numbers, among girls under 15

How effective are the vaccines?

When trials are analysed together, they show that a full course of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. vaccine in girls and women aged 15-25, who have no evidence of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. infectionInvasion by organisms that may be harmful, for example bacteria or parasites.:

  • Reduces by 86 per cent the risk of developing cervical changes that are likely to progress to cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. (see Cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. tests and diagnosisThe process of determining which condition a patient may have.)
  • Reduces the risk of persistent HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. infectionInvasion by organisms that may be harmful, for example bacteria or parasites. after 12 months by 88 per cent.

These trials lasted for up to 5 years. Their results are very encouraging and seem to show that vaccination creates a stronger immune response than natural infectionInvasion by organisms that may be harmful, for example bacteria or parasites..

It is not possible from this information, however, to be certain that HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. vaccination prevents cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body.. The longest follow-up after vaccination has been for 6.4 years and an initial report confirms that high levels of antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. and protection against the more serious changes in the cervixAny neck-like structure; most commonly refers to the neck of the uterus. that could lead to cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. are maintained.

HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. vaccines have been evaluated in large studies (called randomised controlled trialsStudies comparing the outcomes between one or more different treatments for a disease (or in some instances, preventive measures against that disease) and no active treatment at all (the placebo group). Study participants are allocated to the various groups on a random basis. May be abbreviated to RCT.) in which their effectiveness in preventing cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. has been compared with that of a placebo (an inert substance, containing no drugs, that is used as a control).

The vaccines are not effective as treatments for cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body..

HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. vaccination produces the best results, in terms of antibodyOne of a group of special proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. numbers, among girls under 15. Although clinical trials to assess abnormalities in the cervixAny neck-like structure; most commonly refers to the neck of the uterus. have not been carried out in such young girls, it is reasonable to assume, based on studies in older girls and women, that higher levels of antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. give a higher degree of protection.

Targeting vaccination at this age group, before girls become sexually active, therefore offers the greatest long-term potential for reducing new cases of cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body.; the benefits vary, however, from country to country depending on the extent to which local types of HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. are covered by the vaccine and the number of people that can be vaccinated.

Adverse effects of the vaccines

The side effects of the vaccines are usually mild and include reactions at the site of the injection (the most common side effect), headache, fatigue, myalgiaPain in the muscles., gastrointestinal complaints, itching and a raised temperature.

Vaccines may rarely be associated with a severe immune reaction known as anaphylaxis. The rate of anaphylactic reactions is very low.

There is no evidence that HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. vaccines cause harm during pregnancy or breastfeeding.

Vaccinating boys

Vaccinating boys against HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. would:

  • Reduce the risk of cancers of the penis, scrotum and anusThe external opening of the back passage, the rectum., although these are much less common than cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. of the cervixAny neck-like structure; most commonly refers to the neck of the uterus.
  • Reduce the risk of transmitting infections to girls.

The health benefit of vaccination is less in boys than in girls, and the additional cost involved means it may not be economically justified in some countries.

Is cervical screening still necessary?

HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. vaccination will not provide complete protection against cervical cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body. - at best, it prevents infectionInvasion by organisms that may be harmful, for example bacteria or parasites. with the HPVAn abbreviation for human papilloma virus, a sexually transmitted virus that can cause genital warts and may also have a role in the development of various cancers. types responsible for 70 per cent of cervical cancers. In addition, it is not yet clear whether the protection afforded by the vaccine diminishes over time. Regular cervical screening tests will therefore continue to be essential to detect changes in the cervixAny neck-like structure; most commonly refers to the neck of the uterus. at an early stage, to enable treatment before they progress to cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body..