Silgard is a vaccine. It is a suspension for injection that contains purified proteins for four types of the human papillomavirus (types 6, 11, 16 and 18). It is available in vials or prefilled syringes.
|Table of Contents|
|What is it used for?|
|How is it used?|
|How does it work?|
|How has it been studied?|
|What benefits has it shown during the studies?|
|What is the risk associated?|
|Why has it been approved?|
Silgard is used in patients from the age of nine years to protect against:
- precancerous lesions (abnormal cell growth) in the genital area (cervix, vulva or vagina) and cancer of the cervix that are caused by certain cancer-causing types of the human papillomavirus (HPV);
- external genital warts that are caused by specific HPV types.
Silgard is given according to official recommendations.
The vaccine can only be obtained with a prescription.
Silgard is given to individuals aged nine years or older, as three doses, with two months between the first and second doses, and four months between the second and third doses. If a different schedule is needed, there should be at least one month between the first and the second doses, and at least three months between the second and the third, and all doses should be given within a year. It is recommended that individuals who receive the first dose of Silgard should complete all three doses with Silgard. The vaccine is given as an injection into a muscle, preferably in the shoulder or the thigh.
Papillomaviruses are viruses that cause warts and abnormal tissue growth. There are more than 100 types of papillomavirus, some of which are associated with genital cancers. HPV types 16 and 18 cause approximately 70% of cervical cancers and HPV types 6 and 11 cause approximately 90% of genital warts.
All papillomaviruses have a shell, or ?capsid?, that is made up of proteins called ?L1 proteins?. Silgard contains the purified L1 proteins for HPV types 6, 11, 16 and 18, which are produced by a method known as ?recombinant DNA technology?: they are made by a yeast that has received a gene (DNA) that makes it able to produce the L1 proteins. The proteins are assembled in ?virus-like particles? (structures that look like HPV, so that the body can recognise them easily). These virus-like particles are not capable of causing infection.
When a patient is given the vaccine, the immune system makes antibodies against the L1 proteins. After vaccination, the immune system is able to produce antibodies more quickly when it is exposed to the real viruses. This will help to protect against the diseases caused by these viruses.
The vaccine also contains an ?adjuvant? (a compound containing aluminium) to stimulate a better response.
There were four main studies of Silgard, involving a total of almost 21,000 women aged between 16 and 26 years. Silgard was compared with placebo (a dummy vaccine). The studies looked at how many women developed genital lesions or warts that were due to HPV infection. The women were followed up for around three years after the third dose of the vaccine.
Additional studies looked at the ability of Silgard to prevent infection with HPV types 6, 11, 16 and 18 and genital lesions caused by these HPV types in almost 4,000 women aged between 24 and 45 years, and at the development of antibodies against these HPV types in around 1,700 girls and boys aged between nine and 15 years.
Silgard was effective against precancerous genital lesions of the cervix, vulva and vagina, cervical cancer, and warts related to HPV types 6, 11, 16 and 18.
Looking at the results of all four studies together, out of the more than 8,000 women vaccinated with Silgard who had never been infected by HPV types 6, 11, 16 or 18 before, one woman developed a precancerous lesion in the cervix that might have been due to HPV type 16 or 18. In contrast, 85 of the more than 8,000 women who received the placebo vaccine developed lesions that were due to these two HPV types. A similar effect of Silgard was seen when the analysis also included lesions of the cervix due to the other two HPV types (types 6 and 11).
For external genital lesions due to HPV types 6, 11, 16 or 18 (including warts and precancerous lesions of the vulva or the vagina), the results of three of the studies were looked at together. Two women out of almost 8,000 in the Silgard group developed genital warts, and there were no cases of precancerous lesions of the vulva or the vagina. In contrast, there was a total of 189 cases of external genital lesions out of almost 8,000 women in the placebo group.
The studies also showed that Silgard provided some protection against lesions in the cervix linked to other cancer-causing types of HPV, including type 31.
The additional studies confirmed the ability of Silgard to protect against lesions and HPV infection in 24- to 45-year-old women. The studies also showed that the vaccine stimulates the production of sufficient amounts of antibodies against HPV in girls and boys aged between nine and 15 years.
In studies, the most common side effects with Silgard (seen in more than 1 patient in 10) were pyrexia (fever) and reactions at the site of the injection (redness, pain and swelling). For the full list of all side effects reported with Silgard, see the Package Leaflet.
Silgard should not be used in people who may be hypersensitive (allergic) to the active substance or any of the other ingredients. Patients who show signs of an allergy after a dose of Silgard should not receive further doses of the vaccine. Vaccination should be postponed in patients who are ill with a high fever.