in what ways has technology helped in the discovery of new vaccines? hepatitis a and b for example? Hepatitis B vaccine
Hepatitis B virus causes a life-threatening liver infection that often leads to chronic liver disease and puts people at high risk of death from cirrhosis of the liver and liver cancer. Hepatitis B virus infection is a major global health problem. Worldwide, an estimated two billion people have been infected with the hepatitis B virus (HBV), and more than 350 million have chronic (long-term) liver infections.
A vaccine against hepatitis B has been available since 1982. Hepatitis B vaccine is 95% effective in preventing HBV infection and its chronic consequences, and is the first vaccine against a major human cancer. The vaccine has an outstanding record of safety and effectiveness. Since 1982, over one billion doses of hepatitis B vaccine have been used worldwide. In many countries where 8% to 15% of children used to become chronically infected with HBV, vaccination has reduced the rate of chronic infection to less than 1% among immunized children.
As at December 2007, 171 countries reported that they had included the hepatitis B vaccine into their national infant immunization programmes (two of these countries reported introducing in part of the country only). This is a major increase compared with 31 countries in 1992, the year that the World Health Assembly passed a resolution to recommend global vaccination against hepatitis B.
Hepatitius vaccine combination for both A and B
Twinrix* is a vaccine for both hepatitis A and hepatitis B. It combines two FDA-approved vaccines鈥擧avrix, for hepatitis A, and Engerix-B, for hepatitis B. It protects individuals 18 years of age or older against diseases caused by hepatitis A and hepatitis B viruses. The vaccine is recommended for travelers whose occupation or behavior puts them at high risk for exposure to hepatitis B virus, or who are visiting countries with a high or intermediate rate of both hepatitis viruses, as defined by the Centers for Disease Control and Prevention.
Hepatitis A vaccines
Techniques for growing HAV in cell culture have made it possible to generate sufficient amounts of virus for vaccine production. Several inactivated or live attenuated vaccines against hepatitis A have been developed, but only four inactivated hepatitis A vaccines are currently available internationally. All four vaccines are similar in terms of efficacy and side-effect profile. The vaccines are given parenterally, as a two-dose series, 6-18 months apart. The dose of vaccine, vaccination schedule, ages for which the vaccine is licensed, and whether there is a paediatric and adult formulation varies from manufacturer to manufacturer. No vaccine is licensed for children younger than one year of age.
Three vaccines are manufactured from cell-culture-adapted HAV propagated in human fibroblasts. Following purification from cell lysates, the HAV preparation is formalin-inactivated and adsorbed to an aluminium hydroxide adjuvant. One vaccine is formulated without preservative; the other two are prepared with 2-phenoxyethanol as a preservative. The fourth vaccine is manufactured from HAV purified from infected human diploid cell cultures and inactivated with formalin. This preparation is adsorbed to biodegradable, 150 nm phospholipid vesicles spiked with influenza haemagglutinin and neuramidase. These virosomes are thought to directly target influenza-primed antibody-presenting cells as well as macrophages, thus stimulating a rapid vaccine-induced B-cell and T-cell proliferation in the majority of vaccinees. A combination vaccine containing inactivated hepatitis A and recombinant hepatitis B vaccines has been licensed since 1996 for use in children aged one year or older in several countries. The combination vaccine is given as a three-dose series, using a 0, 1, 6 month schedule.
Hepatitis A vaccines are all highly immunogenic. Nearly 100% of adults will develop protective levels of antibody within one month after a single dose of vaccine. Similar results are obtained with children and adolescents in both developing and developed countries. The protective efficacy of the vaccine against clinical disease was determined in two large trials. Among almost 40 000 Thai children aged 1鈥?6 years the protective efficacy was 94% (95% confidence intervals: 82%鈥?9%) following two doses of vaccine given one month apart. Among approximately 1000 children aged 2鈥?6 years, living in a highly disease-endemic community in the United States, the efficacy of one dose of vaccine was 100% (95% confidence intervals: 87%鈥?00%).
Although one dose of vaccine provides at least short-term protection, the manufacturers currently recommend two doses to ensure long-term protection. In studies evaluating the duration of protection of two or more doses of hepatitis A vaccine, 99%鈥?00% of vaccinated individuals had levels of antibody indicative of protection five to eight years after vaccination. Kinetic models of antibody decay indicate that the duration of protection |
