A virus called human papilloma virus, or HPV is the major cause of cervical cancer. Vaccines to prevent this infection have now been developed and two have been licensed for use within the EU and other developed countries including the USA; one is Gardasil from Merck & Co and the other is Cervarix from GlaxoSmithKline. These vaccines protect against strains of HPV most likely to cause cervical cancer, but are not completely protective against all strains and the screening process will remain an important element of cervical cancer prevention.
Both vaccines target HPV types 16 and 18 which cause about 70% of cervical cancers. Gardasil also includes HPV types 6 & 11 responsible for around 90% of cervical warts.
Facts about the vaccines
The vaccines are highly effective in preventing infection by these specific types of HPV in young women who have not been previously exposed to them. Neither vaccine will treat existing HPV infections or their complications.
The length of protection (immunity) is usually not known when a vaccine is first introduced. So far, studies have found that vaccinated persons are protected for six years. More research is being done to find out how long protection will last and if a booster dose will be needed. In the medium term, screening will still be required to assess the effectiveness of the vaccines.
The vaccine is most effective for girls/women who get vaccinated before their first sexual contact. For this reason national guidelines suggest that it is important for girls to get vaccinated before they become sexually active. In the UK and USA, the guidelines recommend vaccines for all girls between the ages of 11 and 13. Most girls and women above this age group will have not received the vaccination and as a result will still require screening.
Ongoing need for screening
Whilst the vaccines may reduce the incidence of cervical cancer over time, it will still be necessary to screen women. The reasons for this are:
- The vaccine will NOT provide protection against all the types of HPV that cause cervical cancer, so women will still be at risk for some cancers.
- Women over the age of 13 will not be vaccinated and therefore require screening until they are 65 years old
- 20% of women will not be vaccinated
- Vaccine immunity studies cover only 6 years
- Some women may not get all the required doses of the vaccine (or they may not get them at the right times) so they may not be fully immune.
- Women may also not get the vaccine’s full benefits if they had already acquired HPV type 16 or 18 before vaccination.
It is important to realise that whilst current screening methods have helped reduce the incidence of cervical cancer, these methods will not be fit for purpose in an environment with lower incidence through vaccination.