Vaccines Against Viral Diseases: Myths and Realities
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Vaccines Against Viral Diseases: Myths and Realities

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Wed, 09/06/2017 - 15:56

Viruses are responsible for a number of diseases that constitute significant public health problems in Mexico and in the world. It is easy to pinpoint these infections as responsible for creating the most harm to humankind throughout history. Such is the case of smallpox, which until 1980, the year in which it was eradicated, was one of the deadliest and most feared viral diseases, according to the article The Rediscovery of Smallpox. However, there are a number of other viral diseases, such as poliomyelitis, that generated thousands of deaths and led to paralysis in children, or influenza, a viral disease responsible for the 1918 European pandemic that caused a significant decrease in the continent’s population. More recently, AIDS, which prior to its identification caused the deaths of thousands of young people in several parts of the world.

In the past couple of years, new viral infections have captured the attention of different national and international health organizations. Such is the case of the ebola outbreak in three different countries in Africa, the Middle East respiratory syndrome coronavirus (MERS) and the chikungunya and zika viruses in the Americas. Without going too far, the zika virus generated a global health alert, according to the WHO, due to its association with microcephaly in newborns and with Guillan-Barré syndrome in adults.

It is important to note that the wide geographic spread of high pathogenic types of viruses that infect birds, such as the H5N1 and H7N9 influenza viruses, represent a constant threat to global public health. In addition, the possibility of facing new zoonotic events increases due to the accelerated growth of the world’s population and its expansion. Climate change, environmental changes and the destruction of the habitat of several species generate new opportunities for disease transmission. The prior has led to the creation of the One Health Concept, in which direct connections are made between people’s health and the wellbeing of animals and the environment.

There are a number of viral infections that usually present themselves in human beings, such as measles, chickenpox, rubella and papilloma, among others. It is the duty of all countries to guarantee public health through prevention measures, as well as the proper and timely diagnosis and treatment of patients, epidemiological monitoring for detection and control of epidemics caused by viruses. 

The strategies for the control of viral infections are initiated with the development of diagnosis methods, design and preparation of vaccines. Should the virus have an animal reservoir or be transmitted by vectors, a strategy designed for vector control is required. All control strategies should be based on the knowledge of the virus’ structure, the nature of its genetic material, mechanisms to enter the organism and replicate within the target cells and the pathogenesis mechanisms.

For those viral infections that have been present among the human population for a longer time, such as rubella, mumps, measles and chickenpox, health systems have developed not only efficient monitoring systems but also vaccines to prevent the disease. Vaccination against some viruses such as polio have been so efficient that the last poliomyelitis case in the Americas was recorded in 1991.

Vaccines are no more than a biological mix containing virus' proteins or a virus’ genetic material that allows the generation of acquired immunity (protection) against a disease. The first vaccine generated was against smallpox and used the cowpox virus, a smallpox variant that generated a slight infection in humans but that could induce protection against the lethal human smallpox. The experience of the vaccine against smallpox led to the generation of other vaccines against diseases such as rabies, yellow fever, polio, measles, mumps, rubella, chickenpox, papilloma, hepatitis A, hepatitis B and influenza. Countries like Mexico entered the 21st century with a national vaccination scheme of wide coverage that includes hepatitis A, hepatitis B, poliomyelitis, rotavirus, measles, rubella, mumps, papilloma and influenza viruses. Unfortunately, not every country guarantees vaccination compulsion nor offers them free of charge. This has led to the continued appearance of a number of preventable diseases in the population.

Another aspect that has contributed heavily in the last years to the appearance of vaccine-preventable infections has been the misinformation surrounding vaccines as a leading cause of autism. Even though the report that once related vaccination with autism has been totally refuted, as mentioned in the article Safety of Vaccines used for Routine Immunization of US Children, a significant number of parents have decided that it is more natural to permit their children to immunize through the infection. These decisions have resulted in significant consequences, such as the presence of measles and mumps among college students in the US or in children visiting Disney parks.

Misinformation regarding vaccination can have important global consequences. If a population is protected with a vaccine, the virus will not multiply in that specific population and vaccinated individuals can travel to any part of the world without the risk of getting sick. Nevertheless, if some members of the population choose to not vaccinate, there will be individuals susceptible to the disease, which will allow the virus to incubate in certain locations. Hence the importance of not straying from the efforts that have been made to overcome these diseases.

Vaccines can be of several types. Attenuated vaccines are made up of live viruses that will not generate serious infections in human beings but which can help the body to produce antibodies that will prevent the infection from occurring. For instance, an attenuated vaccine is the oral vaccine against polio or yellow fever. A second type of vaccines is made of deactivated viruses, in which viruses are treated with chemical compounds that destroy the virus but not its proteins, allowing for the creation of antibodies that protect against the virus but that do not cause the disease. These vaccines are very safe, such as the Salk vaccine against polio. A third vaccination type is made of recombinant proteins, which only use certain proteins from a virus to generate immunity. The organism generates antibodies against the virus’ proteins and is thus protected against them. These vaccinations are fairly safe because they do not generate the disease in order to protect the body from it. An example of this sort of vaccination is that used against human papillomavirus. DNA vaccines are the fourth type, in which organisms are immunized through a DNA sequence that can replicate the virus’ proteins. When the DNA sequence enters the body, it introduces itself within certain cells that will generate the viral proteins against which antibodies will be created. Though this type of vaccinations is still in an experimental phase, results have been promising.

Unfortunately, there are a number of viral diseases for which there are no vaccines. This is due to the fact that viruses have a high mutation rate, which means that whenever a vaccine is ready for a certain virus, a new variant of the virus appears and the antibodies created are unable to avoid the infection of the mutant virus. This has been, among others, one of the reasons why we still do not have a vaccine against the AIDS virus, though it has been in the works for the last three decades.

Although Mexico has done a good job in terms of public health to battle virus-generated infections, the country still faces millions of annual cases of respiratory infections different from influenza, calicivirus gastroenteritis or dengue epidemics. Even now, the country faces viral infections such as chikungunya and zika for which no vaccine has been developed. That is the reason why, within public health budgets, the mortality and morbidity rates associated with viral infections, continue to be considerable. We should not let our guard down regarding the prevention of those diseases that have an available vaccine. Misinformation can contribute to misguided decisions and hurt the population most susceptible to being affected by a serious disease, such as children.

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