ABSTRACT
Among the foremost cost-effective approach to put a stop to viral infections are vaccines, vaccines have proven useful particularly against viral infections causing which includes acute, self-limited infections or chronic infections. For these, it’s must be adequate for the vaccine to act as a natural virus. However, viruses causing chronic infection don’t induce an immune system reaction sufficient to clear the infection, and, as a result, vaccines for these viruses must prompt more effective responses both in quantitative and qualitative perspectives to work than does the natural virus. Here in this review, we study the immunologic and virologic basis for vaccines against viruses and how viruses replicate within host cells and spread infection.
KEYWORDS
Vaccines; Viruses; Infections; Immune system; Microbes
INTRODUCTION
What are Viruses?
Viruses are very small microorganisms, ranging in size from about 20 to 400 nm in diameter. Billions can be adjusted on the head of a pin that’s what their size is. Some of them are rod-shaped; others are round and 20 sided; and still, others have fanciful forms, with multisided “heads” and cylindrical “tails.” In general, Viruses are simply packets of nucleic acid, either DNA or RNA, surrounded by a protein shell and sometimes fatty materials called lipids. Without a living cell, a virus is an inactive particle, lacking the nutrients necessary for reproduction. Only when it enters a host cell it is active, the virus takes control of the host cell’s metabolic machinery to produce copies of itself that may burst out of infected cells or simply bud off a cell membrane. This ability of the virus to depend on host cell nutrients to reproduce makes that the viruses cannot be cultured in artificial media for scientific research or vaccine development; they can be grown only in living cells, fertilized eggs, tissue cultures, or bacteria.
An electron micrograph of an influenza virus particle, showing details of its structure.
Pathogenesis
Viral pathogenesis is the process by which viruses produce disease in the host. Viruses are responsible for various diseases, for example, most of the time viruses cause the common cold, measles, chickenpox, genital herpes, and influenza. Many of the emerging infectious diseases, such as AIDS, SARS, and currently Covid-19 all are caused by viruses. Viruses are only capable of causing disease when they reach the host’s primary physical and natural protective barriers; evade local tissues and immune system; spread in the body, and kill cells either directly or via immune and inflammatory responses. [1]. An important point of viral pathogenesis involves viral epidemiology, which allows physicians to learn the distribution and determinants of disease in human populations. Understanding the factors that influence the development and spread of infectious disease are important for developing preventive and controlling methods. Infection in a population can be endemic, epidemic or pandemic. Infection can be direct, for instance, the respiratory spread of influenza virus, or indirect, for example, arboviruses transmission involving a mosquito vector [2].
Virus Replication
As viruses are obliged for intracellular pathogens they cannot replicate without the machinery and metabolism of a host cell. Even though the replicative life cycle of viruses differs greatly among species and types of the virus, six basic stages are essential for viral replication.
1. Attachment: Viral proteins on the capsid or phospholipid envelope interact with specific receptors on the host cell surface. This specificity defines the host range of a Virus.
2. Penetration: The process of attachment to a specific receptor can induce conformational changes in viral capsid proteins, or in the phospholipid envelope, that results in the fusion of viral and cellular membranes. Some DNA viruses can also enter the host cell through receptor-mediated endocytosis.
3. Uncoating: The viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid.
4. Replication: After the viral genome has been uncoated, transcription or translation of the
viral genome is initiated. It is this stage of viral replication that varies greatly between DNA and
RNA viruses and viruses with different nucleic acid polarity. This process finishes in the de
novo synthesis of viral proteins and genome.
5.Assembly: After de novo synthesis of viral genome and proteins, which can be posttranscriptionally altered, viral proteins are packaged with newly replicated viral genome into new virions that are ready for release from the host cell. This process can also be referred to as maturation.
6. Virion release: There are two modes of viral release: lysis or budding. Lysis results in the
death of an infected host cell, these types of viruses are referred to as cytolytic. An example is
variola major also known as smallpox. Enveloped viruses, such as the influenza A virus, are
typically released from the host cell by budding. It is this process that results in the attainment
of the viral phospholipid envelope. These types of viruses do not usually kill the infected cell and
are called cytopathic viruses. After virion release, some viral proteins remain within the host’s cell membrane, which acts as potential targets for circulating antibodies. Residual viral proteins that remain within the host cell’s cytoplasm can be processed and presented at the cell surface on MHC class-I molecules, where they are recognized by T cells [3].
Viruses can be spread by the direct transferal of blood, and by communication of a wounded cell with a healthy one. Beginning in December 2019, Covid-19, This new virus spreads incredibly quickly between people, due to direct contact with an infected person– no one on earth has immunity to Covid-19 because no one had Covid-19 until 2019. The WHO declared Covid-19 a pandemic in March.
Vaccines
What is a Vaccine?
A vaccine stimulates your immune system to make antibodies, specifically like it would if you
were infected by microorganisms. There are several types of vaccines made in different methods. Some vaccines include parts of microbes], a weakened, or a killed microorganism. Currently, some vaccines contain a strand of RNA (mRNA), which gives cells instructions to produce antibodies against the proteins of a virus. RNA vaccines do not contain any part of the virus itself. In all types, vaccines help your body’s immune system to learn how to defend against the microbes target, including building antibodies against the germ. After getting vaccinated, you acquire immunity to that disease, without having been infected with the microorganism. Vaccines protect you from specific viruses So, you need different vaccines to protect against different viruses. Unlike antibiotics or other medicines that cure infections, vaccines prevent infections [4]. Vaccines in use today often have targeted diseases that were once common in the United States. These diseases include tetanus, hepatitis A, hepatitis B, rubella, measles, and whooping cough. Vaccines have helped us wipe out smallpox globally, a disease that killed 300 to 500 million people in the 20th century. We are very near to fully wiping out polio using vaccines. Regular immunization is a fundamental principle for controlling vaccine-preventable diseases. There are many vaccines recommended for children and for adults to maintain health and prevent disease. Public health agencies and expert medical groups recommend that everyone ensure that they are up to date with routine vaccinations, even during the coronavirus pandemic. For example, if you haven’t had a flu shot this season, it would be important to get one. If you are worried about staying safe during healthcare visits, ask the office about their safety practices. Research continues on vaccines against COVID-19, known as the SARS-CoV-2 virus [5].
How Vaccines Work to Prevent Infections
Some people are at greater risk to become severely ill from some viruses or bacteria, also
Called pathogens. If a pathogenic microorganism gets into the body, our immune system responds. One of the ways our immune system fights infections and prevents future infections
by the same pathogen is by making antibodies. Antibodies are proteins that the body produces
to protect us from a specific germ. We have thousands of different antibodies in our bodies.
Our immune system naturally responds to the new germs that enter our body and make antibodies that seize on to and destroy the pathogens. Vaccines stimulate our immune system
to make specific antibodies to fight off specific germs, such as measles. The new COVID-19 vaccine provokes your body to make antibodies against the “spike protein” on the Coronavirus. Your immune system will still attack the harmless form of bacteria or virus from the vaccine and will produce antibodies to fight it off. The immune system then keeps a memory of the disease, so if a vaccinated person encounters the disease years later, their immune system is ready to fight it off and prevent an infection from developing.
Conclusion
Vaccines continue to be one of the most effective methods to prevent morbidity and death from pandemics and emerging threats. Recent advances may signal another golden age of vaccines. Nevertheless, misinformation and the consequent mistrust of vaccinations pose a threat to their progress and positive impact on global human health. More than ever, it is essential for scientists to communicate scientific facts and to educate the public about the safety and benefits of vaccination using traditional and social media. Therefore, in the future, vaccine science must not only draw from disciplines such as virology, immunology, bioinformatics, and systems biology but also social sciences.
References
- Drexler, Madeline, and Institute (US). 2021. “How Infection Works”. Ncbi.Nlm.Nih.Gov. https://www.ncbi.nlm.nih.gov/books/NBK209710/.
- “Pathogenesis Of Viral Infection | Sherris Medical Microbiology, 6E | Accessmedicine | Mcgraw Hill Medical”. 2021. Accessmedicine.Mhmedical.Com. https://accessmedicine.mhmedical.com/content.aspx?bookid=1020§ionid=56968680.
- “Virus Replication | British Society For Immunology”. 2021. Immunology.Org. https://www.immunology.org/public-information/bitesized-immunology/pathogens-and-disease/virus-replication.
- Iwasaki, Akiko, and Saad B. Omer. 2020. “Why And How Vaccines Work”. Cell 183 (2): 290-295. doi:10.1016/j.cell.2020.09.040.
- 2021. Thoracic.Org. https://www.thoracic.org/patients/patient-resources/resources/covid-19-vaccines.pdf.