PROMISE OF A NEW VACCINE FOR THE HUMAN PAPILLOMAVIRUS AND OTHER INFECTIONS IN HUMAN POPULATION

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Perineal warts is caused by infection with the human papillomavirus, a cancer-causing virus that is responsible for causing cancer in women. A new vaccine has been licensed for the protection against an infectious disease that is a major cause of cancer in women. This vaccine called Gardasil, protects against infection by human papillomavirus (HPV). Gardasil has been licensed and recommended for women entering puberty and older. Various strains of HPV infect up to 75% of sexually active individuals and cause genital warts and vulvar, vaginal and cervical cancers in infected women.

The vaccine is targeted to HPV Types 6, 11, 16, and 18. Together, these strains account for 70% of cervical cancers and 90% of genital warts.

The quadrivalent HPV vaccine is a preparation of viruslike particles (VLPs) of the major L1 capsid proteins from these strains. The L1 proteins have been genetically engineered to be expressed by the yeast Saccharomyces cerevisiae and are released by disruption of the recombinant yeast cells as self-assembled VLPs. After purification, the VLPs are adsorbed onto a chemical adjuvant. The adjuvant immobilizes the VLPs, enhancing their ability to be taken up by phagocytes after injection.

Clinical trials have shown that the HPV vaccine is highly protective against viral infection, including genital warts and all forms of cancers caused by the targeted HPVs. Because HPV is responsible for so much cervical cancer, risk in the immunized population will be significantly reduced. However, perhaps as important, the herd immunity resulting from immunization of a large proportion of the population will stop the spread of these viruses, providing protection even for individuals who are not immunized. Herd immunity is defined as the resistance of a group to a pathogen as a result of the immunity of a large proportion of the group to that pathogen.

This vaccine is currently recommended for girls and women ranging in age from pre-puberty to the end of their reproductive years. While immunization of these susceptible individuals will certainly contribute to disease prevention, herd immunity can be raised to meaningful levels by immunizing all potential HPV sources such as the sexual partners of the women: The immunization of boys and men could provide the herd immunity necessary to eliminate transmission of this preventable STI (sexually transmitted infection) called HPV infection.

Another newly released vaccine is protective for infection by rotavirus, a common enterovirus that causes severe diarrhea, resulting in dehydration and even death in children worldwide. This intestinal disease can now be prevented by immunization with multiple doses of an oral, attenuated Rotavirus. An earlier Rotavirus vaccine was recalled due to postimmunization complications. The HPV and Rotavirus vaccines are two examples of effective vaccine development and implementation, but a number of important infectious diseases still cannot be prevented by vaccination. This list includes tuberculosis, malaria, and HIV, arguably the three most important infectious diseases worldwide in terms of total disease and death. Over 1 million people die each year from each of these diseases globally.

The current tuberculosis vaccine, BCG is considered inadequate and is not administered in many countries. No vaccine exists for the other diseases, although several vaccines are in development, and there are clinical trials for each of these. Finally, Gardasil is the only vaccine that is effective against any sexually transmitted infection in humans. Even some effective vaccines have serious limitations. For example, influenza vaccines are only useful for one year because they are designed to target the strain-specific H and N antigens currently in circulation.

Development of a universal influenza vaccine that targets a common influenza virus antigen, M1, has been proposed, as in theory it should induce immunity to all influenza strains with a single vaccine. The immunogenicity and protection against influenza provided by M1 and other common antigens is, however, unproven.

Further reading

Madigan M.T., Martinko J.M., Dunlap P.V and Clark D.P (2009). Brock Biology of Microorganisms, 12th edition. Pearson Benjamin Cummings Inc, USA.

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