Over last several decades, vaccination has saved millions of lives. Vaccination is one of the most effective ways to prevent diseases and illnesses.
A worldwide vaccination programme helped eradicate smallpox in 1977. In 1796, an English physician, Edward Jenner, observed that milkmaids who had contracted cowpox from cows were not getting infected with smallpox. He inoculated an 8-year old boy with the pus from cowpox blisters and the concept of vaccination was born. Jenner coined the term vaccination after vacca, the Latin word for cow. Vaccines come in many forms. Jenner used a live virus in his vaccine. Another type of vaccine uses viruses rendered inactive chemically or by heat or by radiation. The most famous example of this is the polio vaccine.
The vaccination is now a beacon of hope against novel coronavirus disease (COVID-19) that is rampaging across the globe spreading fear and death.
How Does Vaccination Help Fight Diseases?
Pathogens, the collective name in medical jargon for viruses, bacteria, microbes and all such nasty organisms responsible for our suffering, have proteins known as antigens on their outer surfaces. When pathogens invade our body, the immune system recognises these antigens and start preparing for a battle to get rid of the invaders. Vaccines are biological preparations of targeted antigens, which when introduced into our body, confer immunity, often lifelong, against a specific disease. Vaccination helps the immune system remember what to do should the real virus appear. A high vaccination rate in a community also confers protection through the phenomenon of Herd Immunity. 25 vaccines are currently available against deadly diseases like chickenpox, rabies, diphtheria, tetanus, measles, rubella, hepatitis.
Vaccines made from the whole pathogens, live or dead, were very effective in provoking the desired immune response in our bodies. But they were not completely safe. A new class of vaccines, called subunit vaccines, solved this problem by using only a part of the pathogen, specifically a protein derived from it. Conjugate vaccines linked this isolated protein chemically with a carrier protein and because of their high safety levels became the mainstay of infant immunisation programmes. The improvement in safety, however, came at a loss of efficacy. To boost the effectiveness, ingredients called adjuvants are added to vaccine formulations. Another important requirement of vaccines is their thermal stability during transportation and storage. This requires a reliable refrigeration system.
The progression of a vaccine from development to commercial production is arduous and strewn with failures. Vaccines have to go through a daunting process of pre-clinical and clinical trials. Pre-clinical trials are carried out on animals. Clinical trials are in 3 phases. The first phase establishes its safety. During phase 2 trials, scientists determine if the vaccines really protect and if there are any side reactions. And in phase 3, the viability of large scale manufacturing is established. All these trials have to be carried out under the watchful eyes of the regulatory authorities.
Large-scale manufacturing of vaccines is a complex process consisting of many steps. It starts with growing the selected animal or bird cells through a process of fermentation in a series of bioreactors under a precisely controlled environment. When the cells have grown to a desired number, they are infected with the target pathogen. When the pathogens have multiplied adequately, they are harvested from the growth medium. Next comes a series of stringent purification steps. Vaccines are administered to millions of perfectly healthy people and hence the quality requirements are exceedingly stringent. Impurities from the glass of vials in which they are finally filled and their rubber stoppers are also a matter of concern.
First-generation vaccines were very effective, but we did not fully understand their mechanism. With improved knowledge of molecular biology, the science of vaccines has evolved. In 1980s, genetic engineering was used to make a recombinant vaccine. This involved introducing the DNA from the target virus into another virus to produce the active ingredient for the vaccine. This technique was successful for the vaccine against Hepatitis B. The logical advancement of this approach was to consider introducing the DNA or RNA containing the requisite genetic information to build the antigen in our body itself. Our bodies could be converted into in-situ vaccine factories. The advantages of such an approach are enormous. These include improved immunity response, better thermal stability, absence of infectious contaminants and relative ease of large-scale production.
Vaccine Trials for Coronavirus
Trials are underway in more than a dozen laboratories across the world to develop a vaccine for coronavirus.
Though none of the DNA or RNA based vaccines have been granted a commercial license so far, they are our best bet against the ravaging SARS-CoV-2 virus. Many of the current trials underway have adopted this approach. Moderna Therapeutics of USA created an industry record by identifying the vaccine candidate just 42 days after the genomic sequence of the virus was announced. The company’s product is a synthetic RNA that will persuade our immune system to create antibodies that will fight SARS-CoV-2. Other biotech companies are trying out techniques that are very similar to that of Moderna. A Japanese company is attempting to make a vaccine out of antibodies harvested from the blood of those who have recovered from COVID-19. These novel approaches to fight the novel coronavirus could be the harbinger of a new vaccine technology that will save the human race from similar scourges in the future.
(The author is a chemical engineer and a science writer.)
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