COVID-19 is a disease caused by a new coronavirus called SARS-CoV-2. The world came to know of this virus a year ago when many cases of ‘viral pneumonia’ appeared in Wuhan, People’s Republic of China. This disease rapidly spread across the globe within a year and caused more than 17 lakh deaths. The most common symptoms of this disease are fever, dry cough, and fatigue. It may lead to shortness of breath, chest pain, loss of sense of smell and taste, delirium, and stroke in severe conditions. Of all the patients who tested positive for covid-19, more than 80% recover from the disease without needing primary treatment. About 15% become seriously ill and need a supply of oxygen for recovery. Of all, 5% become critically ill and may experience respiratory failure, acute respiratory distress syndrome (ARDS), septic shock, clots, and failure of heart, liver, or kidneys. Anyone can get infected with coronavirus and die due to it. There is no definite treatment for this disease, and hence the development of a vaccine is the most critical step in the fight against the Covid-19 pandemic.
A vaccine is a blessing in disguise. It is a biological material that provides active acquired immunity against infection. Active acquired immunity is usually long-lasting protection generated by the body in the presence of an infectious microorganism. The vaccine generates such immunity in the body by an agent that is similar to a disease-causing microorganism. This agent is called antigen is either a weakened or killed forms of the microbe (virus), its toxins, or one of its surface proteins.
In blood, antigen from the vaccine communicates with the antigen-presenting cells (APC). These APCs pass the information of the antigen to the immune cells of the body. These immune cells are B cells and T cells. These cells get activated when the APCs communicate the antigen information to them. The activated B cells generate antibodies that bind with the antigen and destroy them, and the activated T cells become cytotoxic (cell killers), which kill the APCs containing the antigen. Thus B and T cells, activated by the APCs, eventually kill the virus in the fight. It is the vaccine that trains them to fight the virus by planning a mock fight. Interestingly, once activated, T cells and B cells remember the antigen’s nature (virus in this case) and convert themselves into memory T cells and B cells. Thus, the immunity against the virus is stored for a long time in the body.
Human genetic information is stored inside the DNA (deoxyribonucleic acid) in the nucleus of the cell. The cell uses this information and copies it into messenger RNA (mRNA or messenger ribonucleic acid). This mRNA comes out of the nucleus and directs the cellular machinery to make individual proteins according to the original code given to it by the DNA. The coronavirus is a globular (ball-like) protein structure that has spikes on its surface. The human body recognizes these spikes as the antigen.
Currently, scientists the world over are making coronavirus vaccines using five different technologies. In the first case, the antigen used in the vaccine is a live but attenuated virus. It means a modified virus that can still replicate and produce immunity in the body, but it does not cause the disease. This technology is used in preparing tuberculosis or Bacille Calmette-Guérin (BCG) vaccine. The second method is to use a whole virus killed by chemicals, heat, or radiation as an antigen. Rabies or hepatitis vaccines are examples of such vaccines. The third kind of technology uses viral protein or virus-like particle made up of proteins as the antigen. This kind of technology does not employ the use of DNA or RNA. Novavax is currently conducting a phase 3 clinical trial for this kind of vaccine for Covid-19. The fourth kind of vaccine is called the viral vector vaccine. It uses another harmless virus to carry the genetic code of the infectious virus. Once inside the human body, this code can instruct the human cells to make the antigen. This technology makes the Ebola vaccine. Currently, Oxford (or Astra-Zeneca, Serum Institute of India) coronavirus vaccine is made using this technology.
The fifth type of vaccine is called the mRNA vaccine. Here, the vaccine contains a lipid nanoparticle covering an mRNA strand that can give cells the instructions to make the antigen. The Moderna or Pfizer vaccines use this technology. This kind of vaccine has much potential. Since no viral material is used (the mRNA is artificially synthesized in the laboratory), no purification or virus processing is needed. Hence, it can be made fast. However, since mRNA material is fragile, it must be stored at very low temperatures ( -70o to 80oC).
The sequence (the arrangement) of amino acids on the coronavirus’s spike protein is now known. This sequence information is used to make an artificial mRNA in the laboratory (Normally, the mRNA directs the protein synthesis. In this case, reverse engineering makes mRNA from the protein’s information). The mRNA is packaged into a lipid nanoparticle. Because of the lipid nanoparticle protection, the mRNA can be injected into the human body without damage. This nanoparticle then fuses with the human cells and releases mRNA in the human cells. The mRNA directs the human cell to make the spike protein. The spike protein made in the human body is then presented by the antigen-presenting cells for the activation of T cells and B cells.
Currently, more than 50 vaccines are in clinical trials across the globe. More than 150 vaccines are being discovered in the laboratories. Some vaccines have received the emergency use permission for the frontline healthcare and public care workers.
Covid-19 is an unforeseen pandemic. But the way the healthcare community has collaborated to fight this calamity is very comforting. The genetic code of this virus was revealed in January 2020. A large amount of funding through grants and government subsidies poured in and now we have vaccines approved for emergency use before the dawn of 2021. Though this is not the end of the war, but it demonstrates the undaunting spirit of humankind.