Currently available live attenuated vaccines include measles, mumps, rubella, oral influenza, oral typhoid, chickenpox, shingles, BCG and yellow fever. Vaccinia (smallpox) is no longer given and live oral polio vaccine is only used in special circumstances. Live vaccines should not be administered to immunologically weakened patients, especially those with depressed cell-mediated immunity, including SLE. The conditions under which live vaccination of patients should be avoided are listed in Table 11-14. In addition, household contacts of immunocompromised patients should not receive live oral polio vaccine, as the live attenuated strain in the gastrointestinal tract can revert to the wild type and spread via the faecal-oral route. Viral vector vaccines use a harmless virus to provide host cells with the genetic code of the antigen designed to fight the immune system. “It`s basically a gene delivery system,” says Dr. Scully. It provides information about the antigen that triggers the body`s immune response.3 Live attenuated vaccines contain a version of the live virus that has been weakened enough not to cause serious illness in people with healthy immune systems. Examples of live attenuated vaccines include measles, mumps and rubella (MMR) and varicella (varicella) vaccines. The guidelines indicate that non-clinical evaluation of live attenuated vaccines includes an assessment of the degree and stability of attenuation and that tests are performed to distinguish attenuated strains from fully virulent and, ideally, partially virulent strains to assess reversion. The production process is also designed to evaluate the stability of the damping.
The likelihood of exchanging genetic information with non-vaccine strains is also determined. If the wild-type virus is neurotropic or if the vaccine has passed through neuronal tissue, health authorities require that an assessment of neurovirulence during non-clinical development be included in a model that distinguishes wild-type strains from fully or partially attenuated strains. Small animal models may be acceptable for this purpose, provided they are susceptible to wild-type viruses. Programmes involving live attenuated vaccines based on genetically modified organisms shall also include an environmental risk assessment, including the possibility of shedding vaccine organisms after administration. There are different types of vaccines. Each type is designed to teach your immune system how to fight off certain types of germs — and the serious illnesses they cause. Attenuated vaccines are “attenuated” versions of pathogens (viruses or bacteria). They are modified in such a way that they cannot cause damage or disease in the body, but are still able to activate the immune system.  This type of vaccine works by activating both the cellular and humoral immune response of the adaptive immune system. When a person receives an oral vaccine or injection, the B cells that help make antibodies are activated in two ways: T-cell dependent and T-cell independent. Response to live vaccines requires an incubation period followed by weeks to months for the development of a strong immune response. Influenza causes seasonal global epidemics every year (see influenza). Various vaccines are available to fight influenza, including inactivated and live attenuated vaccines.
LAIV may offer up to 90% protection in adults under 65 years of age and up to 40% in adults over 65 years of age (although inactivated vaccines are preferred for the elderly). LAIV is usually delivered through the nose, which mimics the natural route of infection of the influenza virus. Live attenuated vaccines developed against polio, measles and mumps are examples of effective vaccines that can provide lasting immunity. Attempts to develop a live attenuated HIV-1 vaccine have been made despite the inherent risks that such a vaccine could be pathogenic or spontaneously revert to a highly pathogenic form. The most impressive protection against SIV challenge to date was created by a live attenuated SIV vaccine administered to macaques (67, 68). However, subsequent animal studies suggesting that a strain of SIV with three deletions (nave, vpr and a negative regulatory element) was pathogenic in newborn and adult macaques (69) stopped the progression of an attenuated living HIV-1 construct into human clinical trials. Oral vaccines or subcutaneous/intramuscular injections are suitable for people over 12 months of age. Live attenuated vaccines, with the exception of rotavirus vaccine, which is administered after 6 weeks, are not indicated for infants less than 9 months of age.
 Live vaccines are highly effective vaccines in preventing a wide range of diseases such as influenza, chickenpox, measles, polio and tuberculosis. Did you know that scientists are still working on developing new types of vaccines? Here are 2 exciting examples: Live attenuated vaccines stimulate protective immune responses when replicated in the host.