Source: africasciencenews.org
Author: staff

In accordance with its mandate to provide guidance to Member States on health policy matters, WHO has issued a series of regularly updated position papers on vaccines and vaccine combinations against diseases that have an international public health impact.

These papers, which are concerned primarily with the use of vaccines in large-scale immunization programs, summarize essential background information on their respective diseases and vaccines, and conclude with the current WHO position concerning their use in the global context.

The papers have been reviewed by a number of experts within and outside WHO and, since April 2006, they have been reviewed and endorsed by WHO’s Strategic Advisory Group of Experts (SAGE) on vaccines and immunization.

The position papers are designed for use mainly by national public health officials and managers of immunization programs. However, they may also be of interest to international funding agencies, the vaccine manufacturing industry, the medical community, scientific media and the public.

Genital HPV infections are primarily transmitted by sexual contact, predominantly but not exclusively through penetrative intercourse. HPVs are highly transmissible, and most sexually active men and women will acquire an HPV infection at some time in their lives.

Whereas most HPV infections are transient and benign, persistent genital infection with certain viral genotypes can lead to the development of anogenital precancers and cancers.

Currently, 2 HPV vaccines are widely marketed internationally. Using recombinant technology, both are prepared from purified L1 structural proteins that self-assemble to form HPV type-specific empty shells or virus-like particles (VLPs). Neither vaccine contains live biological products or viral DNA, so they are non-infectious.

HPV vaccines are designed for prophylactic use only; they do not clear existing HPV infection or treat HPV-related disease. The mechanisms by which these vaccines induce protection have not been fully defined but seem to involve both cellular immunity and neutralizing immunoglobulin G antibodies.

The quadrivalent vaccine, which was first licensed in 2006, contains VLPs for HPV types 6, 11, 16 and 18. The vaccine is produced using yeast substrate and includes amorphous aluminum hydroxyphosphate sulfate as ad juvant.

The formulation contains no antibiotics, thiomersal or other preservatives. This vaccine has been licensed for use in young adolescent girls (as young as 9 years of age in some countries) to prevent cervical precancers and cancers and anogenital warts in females.

In addition, the quadrivalent vaccine is licensed for prevention of vulvar and vaginal precancers and cancers as well as anogenital warts in females. In some countries, the vaccine is also licensed for the prevention of anogenital warts in males.

The bivalent vaccine, which was first licensed in 2007, contains the VLPs of HPV types 16 and 18. It is produced using a novel baculovirus expression system in Trichoplusia ni cells. Each 0.5 mL dose of the bivalent vaccine contains 20 μg of HPV-16 L1 protein and 20 μg of HPV-18 L1 protein adsorbed onto a proprietary ASO4 adjuvant system containing 500 μg of aluminum hydroxide and 50 μg of 3-O-desacyl-4’-monophosphoryl lipid A.

The vaccine contains no thiomersal, antibiotics or other preservatives. This vaccine has been licensed for use in females as young as 10 years of age to prevent cervical precancers and cancers.