Don Syiem and Mayashree B Syiem.
The world first came across coronavirus in 2002-2003 in the form of Severe Acute Respiratory Syndrome (SARS-CoV-1) and later in 2011 by the Middle East Respiratory Syndrome (MERS- CoV). The causative agents for both cases were newly identified coronavirus of zoonotic origin. Both SARS-CoV and MERS-CoV, which emerged in the last two decades, were responsible for epidemics of severe respiratory syndromes. The coronaviruses belong to the genus betacoronavirus and despite their genomic and structural similarities, differ significantly. SARS-CoV and MERS-CoV have a low transmissibility but high lethality, whereas SARS-CoV-2 (COVID-19) has an extremely high transmissibility and its degree of lethality not yet established. The current coronavirus SARS-CoV-2 causing COVID-19 pandemic began in December 2019 in Wuhan (China) and rapidly spread across the globe. The critical point where progression of the disease began, centered on the loss of immune regulation due to exacerbation of the inflammatory components. SARS-CoV-2 has been deciphered in the context of its genome, its origin from bat coronaviruses, and Angiotensin Converting Enzyme-2 (ACE2) as its receptor on the membrane of host cells (where the virus latches on). In human, most coronavirus infections result in mild respiratory symptoms and may be responsible for 20–30% of common colds. The COVID-19 pathological process exhibits a wide spectrum of clinical manifestations, ranging from asymptomatic infections, to mild/moderate common cold-type and finally severe (~15%) infections causing pneumonia accompanied by multi-systemic failure leading to patient’s death.
The entire infectious virus particle, called a virion, consists of the nucleic acid and an outer shell of proteins (envelop). The viral envelope serves several function including protecting the genetic material, facilitating virus entry and evading recognition by the immune system. Coronaviruses have single-stranded positive RNA as their genetic material. The virion envelop (E) contains the spike (S), membrane (M) and the nucleocapsid (N) proteins that protects the genetic material. Protein S is the best studied of the coronaviruses proteins since it contains the Receptor-Binding-Domain (RBD) for binding to the host cell membrane. Binding facilitates the fusion of the virus envelope with the host cell membrane, thus permitting viral gene entrance into the target cells. When it enters host cell, SARS-CoV-2 multiply its genomic RNA (gRNA) and makes nine smaller RNAs that are used for synthesizing various proteins.
The Defense machinery in a Human Body: Our body contains organs of the immune system that play crucial roles in maintaining health and protecting our body from harmful agents, such as viruses, bacteria and other pathogens. The main player in the immune system is the white blood cells (WBC), which screens for invading microbes in the body while travelling through the blood and lymphatic vessels. The lymphatic system is a network of tissues and organs that help rid the body of toxins, wastes and other unwanted materials. The primary function of the lymphatic system is to transport lymph, a fluid containing infection-fighting WBCs. The vessels are connected to lymph nodes, where the lymph is filtered for harmful substances.
Our immune system can be considered in three groups. They are i) Innate immunity ii) Adaptive immunity and iii) Passive immunity. Passive immunity is again of two types a) natural immunity which we receive from our mother and b) artificial immunity that which we receive through medicines. The key difference between innate and adaptive immunity is that innate immunity is a fast response that provides the first line of immunological defense against any infection while adaptive immunity which is mounted against specific invaders is a slow response intercepted by the T and B lymphocytes (classes of WBCs). The innate immune system comprises different cells such as eosinophils, monocytes, macrophages, natural killer cells, tor-like receptors (TLRs) etc. while adaptive immunity consists of highly specialized cells called thymus-derived T lymphocytes and bone marrow-derived B lymphocytes. These cells are capable of recognizing different foreign antigens (foreign structures) in a very precise way and have the capacity to generate immunological memory so that it allows recognizing the pathogens (it’s like carrying a picture) which have been encountered before. However, when our body encounters any germs or viruses for the first time, the immune system does not work efficiently and we tend to fall sick. When the cells of the immune system become educated or trained (due to previous exposures), they become highly efficient in neutralizing the invading pathogens.
The Infection: When the virus starts to propagate, a limited innate immune response is mounted by the body against it and at this stage nasal swabs can help in detecting it. As the virus propagates it reaches the respiratory tract. There it faces a more robust innate immune response. At this stage, the disease is clinically manifested and inflammatory markers called cytokines are produced. The disease will be mild for 80% of the infected patients and mostly restricted to the upper airways. With conservative symptomatic therapy, these individuals may be monitored at home.
The Innate Immune Response: The early defense mechanism of the infected cell is the production of interferons (IFN), chemicals that interfere with viral multiplication. Although coronaviruses are sensitive to IFN, some can still evade the host cell’s initial defense responses. Adaptive Immune Response: The transition between innate and adaptive immune responses lies at a crucial junction where immune regulatory events (still poorly understood) will lead to the development of either a protective immune response or an aggravated inflammatory response. The protective response is T-cell dependent. A dysfunctional response of T-cells that is unable to inhibit viral replication and elimination of the infected cells, may result in an aggravated inflammatory response. This leads to overproduction of inflammatory molecules (cytokine storm), manifested clinically by severe acute respiratory distress syndrome (ARDS).
The Antibody Response: Following viral entry, the body produces protein molecules called antibodies, or immunoglobulins, precisely designed to bind and neutralize specific virus particles. Immunoglobulins are of different classes. Immunoglobulin M (IgM): Found mainly in blood and lymph fluid is the first antibody the body makes when it fights a new infection. Immunoglobulin A (IgA) isfound in the linings of the respiratory tract and digestive system, as well as in saliva, tears, and breast milk. Immunoglobulin G (IgG) is the most common antibody and found in blood and other body fluids. IgG can take time to form after an infection. IgMs and IgAs can be detected early during the 1st week of symptom onset, whereas IgG can be detected at around 14 days after the initiation of symptoms. It is not known how long the protecting levels of these antibodies will remain active. The study of the antibodies against SARS-CoV-2 antigens, in different populations and at various times during the pandemic, has been important in understanding the dynamics of transmission and thus paving the way to development of vaccine.
How Vaccines are made and tested: From Bench to Bedside
The making of a vaccine normally requires at least 10 to 15 years of intense research involving scientists and medical experts from around the world. The first step of this extensive process involves laboratory research. Once the vaccine has been cleared by regulatory authorities, it undergoes at least three more phases of clinical trials on human volunteers to test the vaccine efficacy, dosage, and to monitor for adverse side effects etc. These trials usually take several more years to complete. The last phase involves a test group of up to tens of thousands of human volunteers. However, seasonal flu vaccines are developed on an annual basis.
The Race for corona virus vaccine: Close to 150 vaccines using different technologies and approaches are being developed against SARS-CoV-2 by research teams in companies and universities across the world. Several research groups have already begun injecting formulations into volunteers in safety trials while others are still in the animal testing stage.
Briefly, vaccine or even drug development involves the following steps: (1)Preclinical trial testing(2)Clinical trials (3) Licensed and approval and (4) Distribution. Pre-Clinical trial involves experiments in animals. The aim being to collect data in support of the safety of the new treatment. Preclinical studies are required before clinical trials in humans can be started. Clinical trials are classified into phases: phase I, phase II, phase III and sometimes phase IV. Clinical Phase-I trials evaluate the vaccine safety and toxicity at different dose levels. The trials usually include only a small number of participants (between 20 to 80). Phase-II trials are designed to evaluate the vaccine effectiveness in people and to determine the common short-term adverse effects and risks associated with the vaccine. Phase-III of a clinical trial usually involves up to 3,000 participants. Trials in this phase can last for several years. Phase-IV trials are conducted to determine long-term safety and effectiveness and to identify adverse effects that may not have been apparent in prior trials. Phase-IV trials usually include thousands of participants. Licensing and Approval: Different countries have different regulatory authorities that grant approval and license for a particular vaccine. The U.S. Food and Drug Administration’s (FDA’s) Center for Biologics Evaluation and Research External (CBER) is responsible for regulating vaccines in the United States. While in India, The Central Drugs Standard Control Organization (CDSCO) is the national regulatory body for Indian pharmaceuticals and medical devices.
So, what is a vaccine? Simply put, it is a weakened virus used to stimulate the production of antibodies and provide immunity against its active counterpart. Coming to how vaccines are generated, researchers uses different structures such as the whole virus, the envelop spike protein or the nucleic acid for the purpose. In what is known as virus vaccines, vaccines are developed using the virus itself, in a weakened or inactivated form. In nucleic- acid vaccines, the genetic material and not the whole virus is used. In viral vector vaccines, other viruses such as those causing measles are genetically engineered so that it can produce specific coronavirus proteins. One must understand that these viruses or their structures used for vaccine development are weakened so they cannot cause disease. For developing protein-based vaccines, fragments of proteins or protein shells that mimic the coronavirus’s outer coat can also be used. Many teams are working on vaccines with viral protein subunits- most of them are focusing on the virus’s spike protein or a key part of it called the receptor binding domain.
The frontrunners in COVID-19 vaccine development are spread across the globe. A list of the leading dozen are given here:
- Russia: Gameleya Institute of epidemiology and partners are developing a nucleic acid (mRNA) vaccine. (Status: Registered).
- UK: University of Oxford and AstraZeneca– creating a nucleic acid (mRNA) vaccine named ChAdOx1-S (Status: Phase 3).
- USA: Moderna- nucleic acid (mRNA) vaccine (Status: Phase 3).
- China: Beijing Wuhan Institute of Biological Products and Sinopharm- using inactivated virus (Status: Phase 3).
- China: CanSino Biological Inc. and Beijing Institute of Biotechnology– Adenovirus Type 5 Vector, common cold virus (Ad5-nCOV)
- USA-Germany: Pfizer/ BioNTech/ Fosun Pharma – mRNAs (BNT162b2). (Status: Phase 3).
- China: Sinovac – CoronaVac- Inactivated virus.
- USA, Inovio Pharmaceuticals/ International Vaccine Institute – nucleic acid based vaccine.
- India: Zydus Cadila Healthcare Limited- nucleic acid plasmid vaccine.
- USA: Maryland Biotech company Novavax– Full length recombinant SARS CoV-2 glycoprotein nanoparticle vaccine adjuvanted with Matrix M.
- Australia: University of Sydney & Centenary Institute– attenuated virus, Phase 2
- India, Bharat Biotech is in phase 2 clinical trial with Covaxin using inactivated virus while Serum India Institute (SII) based in Pune will mass produce the Oxford vaccine.
The world is waiting with bated breath and hopes that an effective vaccine comes out at the earliest which on the optimistic side is expected by end of 2020 or early 2021 if the process of licensing and approval by relevant control ing authorities are expedited. If a successful vaccine is created against SARS CoV -2 within the expected period of next six months, this will be then the most fast-tracked vaccine development in history. Let’s hope that the collective efforts by the scientific community and governments come through so that we can breathe again normally.