Vaccine and its science

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By Aditya Sarkar, North Eastern Hill University, India May 12, 2020

The recent coronavirus disease 2019 (COVID-19) outbreak in Wuhan city, Hubei province of China and its rapid international spread has posed a global health crisis [1]. Since, it is a new emerging viral disease, therefore no specific treatments are available. The current response to this crisis involves aggressive implementation of suppression strategies, such as case identification, quarantine and isolation, contact tracing, social distancing and Nationwide lockdown [2]. Various models have been developed using information of COVID-19 cases, suggest that the relaxation of interventions can quickly rebound the transmission [2]. A total of 4.06 million cases with SARS-CoV-2 infections have been confirmed up to date (10 May,2020) and 0.28 million people have died Worldwide [5]. The development of COVID-19 vaccines that can be used globally is therefore a priority for ending this crisis. However, although the term “vaccine” is not very frequent in our daily life. In this article we are going to discuss about various aspects of vaccines.

What is vaccine?                                                                                                                   Chances are you never had the disease tuberculosis. In fact, you probably may not know what tuberculosis is, exactly. Similarly, disease like chicken pox, rubella, diphtheria may be unknown to you. In the 19^th and early 20^th centuries, these diseases were terrifying household words. But today these words are almost forgotten. This change took place largely due to vaccines.

                                                                   Today the term vaccine is used to define all biological compositions, processed from living organisms that boost immunity against a specific disease and either treat or, in most of the cases, prevent the disease [3]. In other words, vaccines are the biological agents that induce an immune response to a specific infectious disease-causing pathogen. Vaccines are provided in liquid form, either by oral, by intranasal routes, or by injection.

How they are made?

In the present scenario, it is well known that a vaccine only can prevent the spread of COVID-19 infection but how would scientists go about creating one? Practically, there are many approaches which are taken to develop vaccines [4]. The approaches are made on the information about infection. Today there are five types of vaccine strategies which are as follows-

• Live, attenuated vaccines from living organisms i.e. virus or bacteria that have been altered so that they can not cause disease. Example of live attenuated vaccine is chicken pox vaccine [6].
• Inactivated vaccines are made by killing bacteria or inactivating viruses by thermal, chemical or other means. The polio vaccine is an example of inactivated vaccine.
• Toxoid vaccines prevent bacterial infections by inactivated toxins of toxin-producing bacteria. Diphtheria vaccine is a sort of toxoid vaccine.
• Subunit vaccines include some specific components of the disease-causing organisms, such as polysaccharides or specific proteins. The vaccine that protects against hepatitis-B is a subunit vaccine.
• Conjugate vaccines are effective against different types of bacterial infections. Here scientists make linkages between polysaccharides and proteins of a bacterial strain to develop an immune response against toxins of the specific bacterium. Haemophilus influenzae type B (Hib) vaccine is a sort of conjugate vaccine [3,6].

How they work and prevent disease?

To understand how vaccines, teach our immune system to provide protection against infections, it helps to first look at how the body fends off and learns from a naturally occurring infection.

                                                                          Our immune system is a complex set of organs and cells that evolved to resist infectious microbes [4]. Blood carries white cells, for fighting off infections and red blood cells, for carrying oxygen to the tissues. These white cells contain macrophages and two major kinds of lymphocytes – T lymphocytes and B lymphocytes [6].

• Macrophages are big white blood cells that grab onto and gobble up as many of the microbes. They digest most parts of the invading microbes except the antigens in our body. The antigens are molecules on microbes that induce immune response in our body, especially by producing certain proteins.
• T-cells are a key component of our immune system that recognise antigens by a surface expressed, T-cell receptor (TCR) [4]. These T-cells are of two types – helper T cell and cytotoxic T cell. The helper T cells secrete the chemical signals to assist the cytotoxic T cells when they come in contact to the foreign antigens while the cytotoxic T cells are offensive in nature and use chemical weapons to attack infection causing microorganisms. The T cells exhibit cell mediated immune response.
• B-cells act like defensive weapon. They produce the large Y-shaped proteins or immunoglobulins (Ig) to invade the foreign particles, called antibodies [7]. The antibodies gather first on the surface of microbes and then stick and coat the microbe. If their shapes are accordant, then they fit to each other like jigsaw puzzle. The antibodies are very specific to their antigens.

The general steps which are followed by a vaccine to prevent an infection and build immune response are given below-

1. The weakened or killed disease causing infectious microorganisms when enter into the body, they induce an immune response.
2. These microorganisms teach our immune system to mimic a natural infection. Since the microorganisms are modified, therefore they are completely unable, or have limited ability to cause disease.
3. The vaccine components or antigens trigger the immune response by producing antibodies. It brings the bad news for the disease-causing microbe. The destruction of microbes is carried out by the binding of antibodies to their specific antigens.

Update of COVID-19 vaccine:

In this current situation the need for COVID-19 vaccine is intensifying globally [13]. Scientists and medical researchers from all over the world are finding a potential vaccine for ending this pandemic. Currently over 110 potential coronavirus vaccines are in different stages of clinical trials out of which 3 vaccines can act as frontrunners of the pack and these are:

• University of Oxford vaccine – One of the most promising vaccines against SARS-CoV-2 has been developed by Jenner Institute and Oxford vaccine group, at the University of Oxford. This vaccine is known as ChAdOx1 nCoV-19. It uses a strain of Chimpanzee adenovirus as vector which causes common cold. This vector is infused with the genetic material of the novel coronavirus present on the surface of the virus [14]. This vaccine is under phase-1 human clinical trial.

• Israel institute of biological research vaccine – on 7th of May, Defence minister of Israel, Naftali Bennett claimed that Israel Institute of Biological Research (IIBR) has developed a monoclonal neutralising antibody which can attack the virus within the bodies of the carriers [15]. Although, it did not specify about human trials.

• Lazzaro Spallanzani National Institute for Infectious Diseases, Italy – Recently in Italy, researchers have stated that they have developed a single dose vaccine which neutralizes the SARS-CoV-2 in the human cells. After a single vaccination in mice, it has been noticed that the developed antibodies are even effective in human beings against the infection [13,14]. 

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References:

1. Jun Lan, Jiwan Ge, Jinfang Yu et al. Structure of the SARS-CoV-2 spike receptor binding domain bound to the ACE2 receptor.
2.   https://doi.org/10.1016/S0140-6736(20)30763-7.
3. http://www.who.int/immunization/position_papers/en/
4. https://www.niaid.nih.gov/
5. https://news.google.com/covid19/map?hl=en-IN&gl=IN&ceid=IN:en
6. https://www.cdc.gov/vaccines/hcp/conversations/index.html
7. Stern Peter L, Leo Oberdan et al. Understanding Modern Vaccines: Perspectives in Vaccinology; DOI: 10.1016/j.pervac.2011.05.002.
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11.  Huang Chaolin,  Wang Yeming  et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China; https://doi.org/10.1016/S0140-6736(20)30183-5.
12. https://neucradhealth.in/language/en/
13. https://timesofindia.indiatimes.com/life-style/health-fitness/health-news/italy-claims-to-develop-first-covid-19-vaccine-here-is-the-current-status-of-all-the-potential-coronavirus-vaccines/photostory/75575319.cms?picid=75575334
14. https://www.moneycontrol.com/news/trends/health-trends/coronavirus-crisis-these-four-covid-19-vaccines-are-ahead-of-the-pack-5247601.html
15. https://www.ndtv.com/world-news/coronavirus-israel-says-made-covid-19-antibody-that-neutralises-virus-in-patients-body-2223695
16. Baruah V, Bose S. Immunoinformatics-aided identification of T cell and B cell epitopes in the surface glycoprotein of 2019-nCoV. Journal of Medical Virology 2020; 92(5):495-500. https://doi: 10.1002/jmv.25698.