Viral Vaccines PDF

Lec. No. 8 Viral vaccines What are vaccines Are drugs used for prevention of disease, by inducing active immunity There are two types of vaccines that induce active immunity: Live attenuated vaccines can replicate inside the body Killed vaccine can not replicate Live Vs killed vaccine Virus in live...

Lec. No. 8 Viral vaccines What are vaccines Are drugs used for prevention of disease, by inducing active immunity There are two types of vaccines that induce active immunity: Live attenuated vaccines can replicate inside the body Killed vaccine can not replicate Live Vs killed vaccine Virus in live vaccine is attenuated by many mechanisms for e.g : 1. the control of human small pox virus by cowpox, 2. yellow fever vaccine is produced by serial passage in heterologous host or cultured cells resulting in numerous point mutations in viral genes and reducing viral virulence and affect tropism 3. influenza vaccine that contains a temperature-sensitive mutant of the virus as the immunogen. The temperaturesensitive mutant will replicate in the cooler air passages of the nose, where it induces IgA-based immunity, whereas it will not replicate in the warmer lung tissue and therefore will not cause disease. Live Vs killed vaccine The virus multiplies in the host, producing a prolonged antigenic stimulus and illicit humoral and cytotoxic T cell immunity Resulting in prolong and great immune response involving IgA, IgG and cytotoxic T cell ,although live vaccines stimulate a long-lasting response, booster doses are now recommended with measles and polio vaccines Live Vs killed vaccine Virus or virus part in killed vaccines can not replicate In the absence of replication, no viral epitopes are presented in association with class I MHC proteins, and the cytotoxic T-cell response is not activated killed vaccines are usually given intramuscularly, and so do not stimulate a major IgA response. Killed vaccines typically do not stimulate a cytotoxic Tcell response, because the virus in the vaccine does not replicate. killed vaccines induce a shorter duration of protection than live vacines and are less protective, and induce fewer IgA antibodies but they are more heat-stable and cannot revert to virulence. Important clinical points regarding viral vaccines Live attenuated vaccine can revert to virulence and pathogenecity in immunized person e.g oral polio vaccines live viral vaccines should not be given to immunocompromised people or to pregnant women, because although the virus is attenuated it can still be pathogenic in a host with reduced immunity. The live vaccine can be excreted by the immunized person., and if the the virus spread successfully it will immunizes others(called herd immunity) as occurs with the live polio vaccine Herd immunity (also known as community immunity) occurs when a sufficiently large percentage of the population (the “herd”) is immunized so that an unimmunized individual is protected continue Certain viral vaccines, namely, influenza, measles, mumps, and yellow fever vaccines, are grown in chick embryos. These vaccines should not be given to those who have had an anaphylactic reaction to eggs DNA recombinant vaccines and DNA vaccines DNA recombinant vaccines : Are purified viral antigens produced from genes cloned in either bacteria or yeasts by recombinant DNA techniques. The three viral subunit vaccines containing purified antigens produced by recombinant DNA techniques are the hepatitis B virus (HBV) vaccine, the human papillomavirus (HPV) vaccine, and the Shinrix version of the varicella-zoster (VZV) vaccine used to prevent zoster (shingles) DNA recombinant vaccines and DNA vaccines DNA vaccines: These vaccines contain purified DNA encoding the appropriate viral proteins genetically engineered into a viral vector or plasmid. Immunization with this composite DNA elicits both antibody and cytotoxic T cells and protects against disease in experimental animals. Adenovirus had been used for SARS cov 2 vaccine Vaccinia virus, adenovirus, and poliovirus, are being used experimentally to immunize against other viruses such as HIV. Home work What is passive active immunity and give examples for? Mention the current viral vaccines used in practice The end