Traditionally, vaccines have been developed for prevention of infectious diseases. An apt example is that of vaccines currently in use for prevention of COVID-19, a viral infection that affects the nervous system. Vaccines for neurologic disorders are not only developed for prevention of infectious diseases, but also for the treatment of cancer involving the nervous system, autoimmune disorders such as multiple sclerosis, and degenerative disorders such as Alzheimer disease. Alzheimer disease and stroke have important inflammatory and immune components and may be amenable to treatment by antiinflammatory and immunotherapeutic approaches. This article reviews various types of vaccines relevant to the nervous system, including adverse reaction of vaccines on the nervous system. An example is the vaccine for Alzheimer disease where the objective is to generate antibodies against amyloid beta. The earlier clinical trials, although effective in halting the progression of the disease, produced encephalitis as an adverse effect in some patients. Improved vaccines are now under development.
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• Vaccines are the most important and effective preventive measures against COVID-19 and its neurological manifestation, ie, neuroCOVID.
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• Apart from prevention of infectious diseases, vaccines are in development for therapeutic use in noninfectious diseases.
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• Indications for therapeutic vaccines include neurodegenerative disorders, traumatic brain injury, glioblastoma, and multiple sclerosis.
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• Vaccines are tested for safety, but adverse reactions may occur, some of which affect the nervous system.
Historical note and terminology
The ancient Chinese practiced variolation, a method of protection against smallpox by intranasal inoculation of a healthy person with a small quantity of scabs from an infected person. Edward Jenner established the scientific principle of immunization in 1796 by using cow pox as a related immunogen against smallpox and introduced smallpox vaccination for human use (Jenner 1798). The first vaccine intended for those people who were already infected (the vaccine for rabies) was tested by Louis Pasteur in human beings in 1881 (33). Robert Koch, the German microbiologist who isolated Mycobacterium tuberculosis in 1882, attempted a therapeutic tuberculosis vaccine, but it was not until 1921 that the most widely known attenuated bacterial vaccine for protection against tuberculosis, bacille Calmette-Guerin, was introduced. This vaccine remains in use today (05). Considerable advances have taken place in vaccination technology in the past 200 years, and vaccines are available for many infections. Vaccination has had its impact on neurologic disorders as well. The most important developments in this respect were the introduction of the polio vaccines: the poliovirus vaccine (44) and the oral polio vaccine in 1961 (43). Currently, poliomyelitis is on the way to eradication.
Vaccines have probably prevented more diseases than any other medical or public health intervention except sanitation. The traditional use of vaccines has been mostly limited to the prevention of disease. The trend changed in the 1990s when several clinical trials were underway for treatment of active infections with viruses such as HIV-1 and the herpes simplex virus. DNA vaccines, which are easy to produce and stable, were the most important development in this area in the last decade. Messenger RNA (mRNA) vaccines are the most important current advance in vaccinology, and the most important examples are mRNA vaccines for COVID-19. Most vaccines take years to develop, and companies are reluctant to take on these projects because of the high cost and high failure rate. Due to the tireless drive of a US president, setting up of operation “warp speed” and investment by the US Government, successful mRNA vaccines for COVID-19 were developed in the record time of 10 months.
Apart from infectious diseases, therapeutic vaccines are in development for cancer, autoimmune disorders (eg, multiple sclerosis), and degenerative disorders (eg, Alzheimer disease). Alzheimer disease and stroke have important inflammatory and immune components and may be amenable to treatment by antiinflammatory and immunotherapeutic approaches including vaccines. Cancer vaccination involves attempts to activate immune responses against antigens to which the immune system has already been exposed. Vaccines are available in various forms and given by several routes of administration. Advances in genomics with sequencing of genomes of infectious organisms are providing opportunities for genetically engineered specific vaccines. This article is a brief overview of vaccines for neurologic disorders. Only active immunization is considered here. Active immunization should be distinguished from passive immunization, which results in immediate protection of short duration and may be achieved by the administration of antibodies themselves in the form of antisera (of animal origin) or immunoglobulins (of human origin).