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Biological defense vaccines are being developed to counter viruses, toxins, bacteria, and genetically engineered biological threat agents. Research activities start with basic research activities and proceed through the following steps such as construction of the infectious clone, identification of attenuating mutations, construction of vaccine candidates, testing in rodent models, testing in non-human primates, final selection, and formulation. The formulated production may then become a candidate for an investigational new drug application for transition to advanced development and clinical trials then ultimately licensed production. An example of a product being developed within the Medical Biological Defense Research Program (MBDRP) of US is the Next Generation Anthrax Vaccine. In cooperation with the National Institutes of Health, the next generation vaccine will provide greater or equal protection, require fewer doses to produce immunity, and have fewer adverse effects than the current anthrax vaccine.
Vaccines have long been used to combat infectious diseases. The last decade has witnessed a revolution in the approach to vaccine design and development. No longer is there a need to rely on the laborious classical methods such as attenuation or killing the pathogen. Now sophisticated technologies are being used like genomics, proteomics, functional genomics, and synthetic chemistry can be used for the rational identification of antigens, the synthesis of complex glycans, the generation of engineered carrier proteins, and much more. Vaccine design and development require cutting-edge research and technologies in vaccine design and development. Particular emphasis is given to new approaches and technologies. New strategies to identify protective antigens, generation of improved adjuvants, use of alternative immunization routes, improving vaccine safety, and finding and establishing the correlates of protection.
Vaccine Development and Implementation requires research to discover new vaccine antigens and novel approaches to immunization takes several years, and costs tens of millions of dollars. Once a discovery is made, several developments must be undertaken to reach the licensing stage. Those developments include process development, to produce an economically viable vaccine, consistently in a manner that satisfies regulators; and clinical development, to demonstrate the safety and measure the protective effect of the vaccine in humans; assay development, to develop the appropriate tests to ascertain the purity, potency and stability of the vaccine under development. Process development is further divided into bulk manufacturing and product finishing. Bulk manufacturing involves the culture of live organisms, followed by separation and purification of the desired antigen. Finishing involves the formulation with either adjuvant and or stabilizer and the filling of vials or syringes.
For any vaccine implementation there is need to take into confidence of public regarding their health issues and vaccine implementation. Public health programs succeed and survive if organizations and coalitions address these key areas such as innovation to develop the evidence base for action; a technical package of a limited number of high-priority, evidence-based interventions that together will have a major impact; effective performance management, especially through rigorous, real-time monitoring, evaluation, and program improvement; partnerships and coalitions with public and private sector organizations; communication of accurate and timely information to the health care community, decision makers, and the public to effect behavior change and engage civil society; and political commitment to obtain resources and support for effective action. Smallpox eradication, tuberculosis control, tobacco control, polio eradication, and other issues have made progress by addressing these key areas only.
Evidence-based guidelines for immunization of infants, children, adolescents, and adults have been prepared by an Expert Panel of the Infectious Diseases Society of America (IDSA). These guidelines are prepared for health care professionals who care for either immunocompetent or immunocompromised people of all ages. Vaccines are now recommended universally for young children, influenza vaccines are recommended annually for all children aged 6 months through 18 years. And a second dose of varicella vaccine has been added to the routine childhood and adolescent immunization schedule. Many of these changes have resulted in expansion of the adolescent and adult immunization schedules. In addition, increased emphasis has been placed on removing barriers to immunization, eliminating racial/ethnic disparities, addressing vaccine safety issues, financing recommended vaccines, and immunizing specific groups, including health care providers, immunocompromised people, pregnant women, international travelers, and internationally adopted children.
Proper vaccine storage and handling practices play a very important role in protecting individuals and communities from vaccine-preventable diseases. Vaccine quality is the shared responsibility of everyone, from the time vaccine is manufactured until it is administered. The success of efforts against vaccine-preventable diseases is attributable in part to proper storage and handling of vaccines. Vaccine management, including proper storage and handling procedures, is the basis on which good immunization practices are built. Vaccines must be stored properly from the time they are manufactured until they are administered. Proper maintenance of vaccines during transport is known as the cold chain. A proper cold chain is a temperature-controlled supply chain that includes all equipment and procedures used in the transport and storage and handling of vaccines from the time of manufacturer to administration of the vaccine.
Live bacterial vaccine vectors have been extensively used to deliver and express heterologous vaccine antigens to protect against cancer and various infectious agents, including AIDS. Live bacterial vaccines have the advantage that they can express multiple antigens are easily mass produced and can be orally or intranasally applied and induce strong immune responses. However, relatively few studies have tested whether heterologous expression of parasitic antigens with bacterial vaccine vector strains can lead to protective immunity. Invasive bacteria such as Salmonella, Listeria, Yersinia, Shigella and Mycobacterium bovis BCG have been used as vaccine vectors, capable of mounting potent humoral and cellular immune responses. Since these are pathogenic bacteria they were attenuated to generate suitable non-pathogenic vaccine strains. Many attenuated strains have been reported that are non-pathogenic and have limited proliferative capacity in vivo.
For the past two centuries vaccines have provided a safe and effective means of preventing a number of infectious diseases. The currently available vaccines are more than a millionfold safer than the diseases they are designed to prevent. Not only are some vaccines available via injection but other vaccines are also given orally or intranasally. New vaccines are being studied for topical and intravaginal use. In addition new systems are being developed for more efficient production of vaccines especially for influenza. Vaccines are currently available for only a limited number of viral and bacterial diseases. In the future, it is anticipated that safe and effective vaccines will be developed against a number of other viral and bacterial infections as well as fungal and protozoan diseases.
There are many known adjuvants in widespread use including oils, aluminium salts, and virosomes. In immunology, an adjuvant is a component that potentiates the immune responses to an antigen and or modulates it towards the desired immune responses. An immunologic adjuvant is defined as any substance that acts to accelerate, prolong, or enhance antigen-specific immune responses when used in combination with specific vaccine antigens. In the early days of vaccine manufacture, significant variations in the effectiveness of different batches of the same vaccine were observed; and correctly assumed to be due to contamination of the reaction vessels. However it was soon found that more scrupulous attention to cleanliness actually seemed to reduce the effectiveness of the vaccines. And that the contaminants (dirt) actually enhanced the immune response.
Plant-derived vaccines have several advantages. They can be produced cheaply in very high amounts, carrier plants such as potatoes and corn are readily accepted by patients and antigens derived from them are stable and can be stored for long periods of time. The likelihood that contamination by a plant virus would have an adverse effect on humans is almost negligible. There are several technical challenges concerning plant-derived vaccines that must be resolved before they can enter wide-scale use and the regulatory requirements for this novel class of vaccines must be established. In addition, public acceptance of the new technology must be ensured. As the development of plant-derived vaccines matures, World Health Organization (WHO) will continue to serve as a forum for the international harmonization of requirements.
Vaccine schedules are developed by governmental agencies or physicians groups to achieve maximum effectiveness using required and recommended vaccines for a locality while minimizing the number of health care system interactions. Over the past two decades, the recommended vaccination schedule has grown rapidly and become more complicated as many new vaccines have been developed. Many vaccines require multiple doses for maximum effectiveness either to produce sufficient initial immune response or to boost response that fades over time. For example, tetanus vaccine boosters are often recommended every 10 years. Some vaccines are recommended only in certain areas or countries or at-risk populations where a disease is common. For instance, yellow fever vaccination is on the routine vaccine schedule of French Guiana is recommended in certain regions of Brazil.
The mucosal tissues of nasal, oral, ocular, rectal, vaginal cover large surface of the body. Since many infections are initiated at mucosal sites, it is critical to develop strategies for neutralizing the infectious agent at these surfaces. Mucosal vaccination involves the administration of vaccines at one or more mucosal sites leading to induction of immune responses at the mucosal site of administration, other mucosal sites, and/or systemically. Most infectious agents enter the body at mucosal surfaces and therefore mucosal immune responses function as a first line of defense. Protective mucosal immune responses are most effectively induced by mucosal immunization through oral, nasal, rectal or vaginal routes, but the vast majority of vaccines in use today are administered by injection.
An HIV vaccine may have the purpose of protecting individuals who do not have HIV, from being infected with the virus of a preventative vaccine, or treating an HIV-infected person with a therapeutic vaccine. There are two approaches to an HIV vaccine. One is an active vaccination approach in which a vaccine aims to induce an immune response against HIV; and the other is a passive vaccination approach in which preformed antibodies against HIV are administered. Sadly, there is no licensed HIV vaccine on the market. However, multiple research projects are trying to find an effective vaccine. There is evidence from humans that a vaccine may be possible. Some of the HIV-infected individuals naturally produce broadly neutralizing antibodies which keep the virus suppressed and these people remain asymptomatic for decades. Potential broadly neutralizing antibodies have been cloned in the laboratory monoclonal antibodies and are being tested in passive vaccination clinical trials.
Several vaccine types can de distinguished among the second-generation veterinary vaccines depending whether they are live or inactivated, according to the strain of rabies virus used and the characteristics of the cell substrate chosen for viral replication. Considerable progress has been made in the production of rabies vaccines whether live or inactivated for animal use during the past two decades with the increasing use of continuous cell lines as a substrate and adoption of the fermentor technology for antigen production. These vaccines are produced for administration to domestic animals or wild species by parenteral or oral routes according to vaccine characteristics. More recently a third generation of live veterinary rabies vaccine has been developed using recombinant technology. Depending upon the expression system these vaccines are used either parenterally or orally. Oral rabies vaccines are widely used in foxes in Europe and in racoons in the USA. Trials are under way for the oral immunization of dogs in developing countries.
The application of genetic and recombinant DNA approaches to vaccination has led to new possibilities of safer and more efficient vaccines. Recombinant DNA technology can be applied to antigen identification and isolation, and by being able to clone and express all the antigens of an organism individually, overcomes two major hurdles associated with traditional vaccines. Nuclear magnetic resonance (NMR), molecular modeling and X-ray crystallography approaches in understanding protein structures has contributed enormously into the generation of improved vaccines. Numerous peptide based vaccines have been shown effective in pre-clinical and in human clinical trials. The advent of these technologies stimulated the production of new vaccines and the identification of precise epitopes on antigens has made synthetic peptide vaccines a real possibility. Such vaccines are designed to be safer and more efficient. Unfortunately, there are still many obstacles for their clinical use; the limited immunogenicity of many of these candidates has hindered their development as potential vaccines. Strategies to enhance the immunogenicity of candidate vaccines are therefore required.
The capacity to prevent more infectious diseases has increased remarkably for several reasons such as new vaccines have been licensed like human papillomavirus vaccine; live, attenuated influenza vaccine; meningococcal conjugate vaccine; rotavirus vaccine; tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis or Tdap vaccine; and zoster vaccine, new combination vaccines have become available for measles, mumps, rubella and varicella vaccine; tetanus, diphtheria, and pertussis and inactivated polio vaccine; and tetanus, diphtheria, and pertussis and inactivated polio/Haemophilus influenzae type b vaccine, hepatitis A. Further WHO's Initiative for Vaccine Research (IVR) facilitates vaccine research and development against pathogens with significant disease and economic burden with a particular focus on low and middle income countries.