Explainer: All About Vaccines


G. N Bhat/ Dr. Nawab John Dar

Vaccines are the biological agents which elicit an immune action in response to an antigen derived from an infectious disease. It trains the body’s immune system so that it can fight a disease that it has not encountered before. First vaccine was developed by Edward Jenner (1796), when he was using cowpox virus (Vaccinia) to inoculate and confer protection against Small-pox in humans. Vaccination is one of the great achievements reducing morbidity and mortality against life threatening diseases like measles, polio, tetanus, diphtheria, tetanus meningitis, influenza and typhoid. Vaccines are often confused with anti-serum, where preformed antibodies taken from another organism to be injected into the blood stream offering temporary protection in a passive manner. However, vaccines provide active immunity where body is prepared to be ready with fighters in a memory induced way and the immune system remembers the first vaccine as imitating infectious agent and remains ready if the pathogen enters in the body in future.

Vaccine Development and Clinical Trials

Vaccine development takes place in two phases, preclinical and clinical setting. Preclinical studies again are conducted in two different paradigms what we call as in vitro and in vivo models. These preclinical studies conducted in laboratory directly using appropriate animal model (in-vivo approach) or human cells (in-vitro approach) are directed to establish the physical, chemical and biological characteristics of the candidate vaccine. These studies may also provide us clues about the possible risks of vaccine and its evaluation in terms of efficacy and safety. However, here we need to keep it mind that all the results we establish from these models does not necessary translate in a similar fashion, when tested in humans, that’s the main reason why most of the drugs/vaccines fail in clinical trials. Next step is clinical research and development of the vaccine which includes three Phases (Phase I, Phase II, Phase III). Phase I of clinical studies includes initial testing of the vaccine on a smaller number of individuals of about 20-30 healthy adults. Phase I studies are primarily concerned with safety and tolerability and other pharmacological parameters of the vaccine. Phase II studies are used to obtain the preliminary information about the vaccines ability to produce the immune response called as immunogenicity in the target population and general safety of the vaccine candidate .The vaccine  is tested on that group of population whose age and health is similar to the people for whom the vaccine is intended to use and produce the immune response, so that the  immunised persons may be monitored to see the response of defence system of the body with respect to the vaccine. The phase III clinical trial is the important one to study where sufficient data have to be obtained to demonstrate that the new product is safe and effective for the desired purpose. The testing of the vaccine may include non- human primates like monkeys because of relative evolutionary closeness to humans and this is possible only if an appropriate disease model is available .The immune response data obtained from the animal model studies can help to select the doses , schedules and routes of administration which are to be evaluated in clinical trials.

Vaccine for COVID-19

Multiple strategies for vaccine development across the globe are progressing rapidly to combat COVID-19. Numerous biological approaches have been in use and some have shown very promising results in pre-clinical studies. Based on these pre-clinical results several companies along with National Institute of Health (NIH), USA have started phase I clinical trials, but so far, there is no vaccine available in market for human use.

The first clinical trial started by USA is a phase I, open-label, dose ranging clinical trial in males and non-pregnant females, 18 to 55 years of age. This clinical trial is designed to assess the safety, reactogenicity and immunogenicity of mRNA-1273 manufactured by ModernaTX, Inc. mRNA-1273 is a novel lipid nanoparticle (LNP)-encapsulated mRNA-based vaccine that encodes for a full-length, prefusion stabilized spike (S) protein of SARS-CoV-2. This study started on March 3, 2020 and the expected end date is June 1, 2021 where 45 participants will be tested. Another hopeful study is going on at University of Oxford, which is based on a chimpanzee adenovirus vaccine vector called ChAdOx1. This study is recruiting up to 510 healthy adult volunteers aged 18-55 years.

Experts have estimated that it will take 12-18 months to develop a new vaccine at high speed. Similarly, China is doing a Phase-I clinical trial, which is based on a recombinant novel coronavirus vaccine that incorporates the adenovirus type 5 vector (Ad5). There are 108 participants between 18 and 60 years old who will receive low, medium, and high doses of Ad5-nCoV. The study is due to complete December 2021. There are several other similar studies based on different biological approaches which are being approved and are actively recruiting participants for the study. We are thankful all those scientists who are working actively and turning every stone to make it possible but at the same time we need to understand and remind ourselves individually and collectively that “There is currently no vaccine in the market and even if the one is developed it will reach us at least after a year”. The better approach to save our lives at the moment is to follow the precautionary measures and cooperate at every level to restrain the spread of this virus.

  • The basic principles for the production and control of vaccines and up to date methods for standardisation of assays for vaccine development are described in Technical Report Series (TRS) of World Health Organisation (WHO).

G. N Bhat is associated with School Education Department, J&K while Dr. Nawab John Dar is a Postdoctoral Fellow, School of Medicine, UT Health, San Antonio, USA.The authors have started their scientific career together and are passionate about writing for general public interest.

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