HPV VACCINE

=HPV VACCINE= ===THE IMMUNE SYSTEM=== [image:http://i.imgur.com/LPmTn3R.png] When we are first infected with a virus the immune system employs a range of non-specific defences including, chemical and cellular responses that try to clear the infection. Once the virus has been processed and the immune system has confirmed that it is a foreign invader we begin to produce '''antibodies''', small proteins that can stick to the virus, deactivate it and tag it for destruction by white blood cells. Antibodies are specific to a particular '''antigen''' –some part of the virus that can be recognized as foreign (usually a surface protein). When we encounter the same virus for the second time specific antibodies can be made much more quickly and can often clear the infection before it gets established and any significant damage is done. ===The HPV Vaccine=== [image:http://i.imgur.com/iJA6Gij.png?1] The HPV vaccine contains only a small part of the virus (the L1 surface protein) that cannot cause infection on its own. The protein is made by inserting the viral gene for the protein into yeast cells (genetic modification). The yeast cells, which have no use for the protein, secrete it and it can then be purified for use in the vaccine. Once injected, the L1 protein stimulates the production of antibodies without actually causing an infection. This results in what is called immune memory. If the actual virus is encountered at a later stage antibodies can be produced more quickly and eliminate the virus before any significant infection is established. The HPV vaccine also contains adjuvants, certain chemicals that stimulate an immune response There are two different HPV vaccines available: *'''Gardasil''' which targets all four of the virus types (16,18,6,11), two of which cause 70% of cervical cancers and two of which cause 90% of genital warts *'''Cervarix''' which only targets two of virus types 16 & 18 which cause 70% of cervical cancers . ===PROS & CONS=== '''Pros:''' *Placebo controlled clinical trial of 20,845 women showed Gardasil prevented 97%-100% of moderate-high grade precancerous lesions. Within one month over 99.5% of individuals had developed antibodies to the target strains *Immunity persists at high levels for at least 5 years after vaccination and may be life-long *A study of approx. 1 million girls found no evidence of any significant adverse effects (such as autoimmune, neurological, and clotting events) '''Cons:''' *The vaccine costs NZ approx $16 million per year *It does not prevent infection of non-target strains (some of which can still cause cervical cancer) *There is a lack of long-term data / proof that immunity is in fact lifelong *There is no benefit to those who have already been infected with the target strains. *In the US approx. 350 adverse events per 100,000 vaccinations have been reported. Just under 9% of these were serious (hospitalization / death). There have been at least 44 reported deaths following the vaccine, of which 27 have been confirmed. However, the vaccine has not been established as the cause of '''any''' of these adverse events.