Understanding Covid Vaccines And Their Effectiveness

Dr. Sanjukta Das

Vaccines are scientific tools that protect us from infections and are so considered to be effective health interventions. Vaccines exert actions by mimicking an infection which alerts and prompts our immune system to fight against pathogens such as bacteria, viruses, fungi and parasites. In the 1970’s Dr Edward Jenner innovated a technique of achieving immunity against small pox by administering cowpox fluid in the human body. This marked the advent of ‘Vaccination’ and ‘Immunisation.’ In fact, the word vaccine derives its origin from the name of cowpox virusVaccinia. Since then, human beings have immensely benefitted from vaccines. At present, in the face of COVID-19 pandemic -one of the greatest health crises in recorded history - the buzz word is vaccine. Thanks to scientific community whose passionate research to innovate and develop vaccines has resulted in more vaccine varieties. The variety of vaccines that have been simultaneously developed to fight the COVID19 is greater in number than any other vaccine ever developed.

Science of Corona Vaccines

The science behind the vaccine against SARS-CoV-2 includes all potential approaches- conventional as well as novel - for ensuring safety and efficacy.

Whole Virus Approach

Inactivated Covid-19 Vaccine: Vaccine platforms based on inactivated microbe is a well-established and time tested approach utilised in developing vaccines against a number of diseases in the past. Jonas Salk in 1950s formulated the polio vaccine on this principle. Other examples of this inactivated vaccine category are the vaccines used for Rabies and Hepatitis A. COVAXIN- India’s indigenous COVID-19 vaccine developed by Bharat Biotech in collaboration with the National Institute of Virology and ICMR is an inactivated coronavirus vaccine capable of inducing immune response in humans. The science behind this vaccine is that the virus is inactivated and replication deficient, but its surface proteins remain intact. The inactivated form of COVID-19 virus is administered with an immunogenic adjuvant to boost immunogenicity. COVAXIN activates both the T and B cell response. The plus points with this vaccine protocol is that it does not need sub-zero storage as it is stable at 2-8 degree Celsius and is ready for use without reconstitution requirement.

Viral Component COVID Vaccines

Viral Subunits Approach: In this vaccine technology, instead of using the entire virus for vaccine development, the specific parts of virus such as protein or sugars are utilised. Vaccines administered to children including those of diphtheria, tetanus, whooping cough (Pertussis), etc belong to this category. Corona vaccines, based on protein subunit formulations include CORBEVAX produced by Hyderabad-based firm Biological E and COVOVAX by Serum Institute of India. CORBEVAX is India’s first indigenously developed RBD (receptor binding domain) protein subunit vaccine against SARS-CoV-2. COVOVAX is a subunit protein vaccine based on NOVAVAX formulation. COVOVAX is based on a novel platform of utilising an engineered insect virus baculovirus containing a gene for spike protein. The baculovirus replicates in moth cells and produce spike proteins. These spike proteins are extracted and purified for use in a vaccine. Unlike mRNA (Messenger RNA) and vector vaccine, subunit vaccine is a protein adjuvant vaccine. Adjuvants are ingredients incorporated in vaccine formulation to enhance immune response. It contains nanoparticles of spike proteins which induce both antibody and T cell response.

Nucleic Acid (DNA/RNA Based) COVID Vaccines

This kind of vaccine platforms uses genetic material having the instructions for the cells to synthesize specific proteins. The examples are ZyCov-D – a DNA based vaccine, PfizerBioNTech’s Comirnaty - an mRNA based vaccine, and Moderna’s Spikevax. These vaccines are injected intramuscularly and thus as the mRNA enters the cell, it instructs the cell machinery to produce spike protein, a viral surface protein which triggers our immune system to produce antibodies against it. Since no live virus is incorporated in it, there is no fear of infection to occur. Additionally, mRNA never enters the nucleus of the cell, so no scope for mutation. However, RNA vaccines need to be stored at ultra-cold temperature of about minus 70 degree Celsius. ZyCov-D is the world’s first plasmid DNA vaccine against COVID19 infection, produced indigenously in India by Zydus Cadila of Ahmedabad with the support of Department of Biotechnology and the ICMR (Indian Council of Medical Research). The science behind this vaccine adopts a novel approach that it uses a genetically engineered, non-replicating plasmid having the instructions for spike protein. On vaccination, the code for spike protein enters the cell and spike protein is produced which stimulates the immune system to build immune response. This vaccine is administered intradermally through a needle-free device that is painless. One positive aspect about DNA platform vaccine is that it can be easily modified to mutation in the Coronavirus. Besides, DNA vaccines have better stability and lower cold chain requirements.

Non-Replicating Viral Vector Based Vaccines

This type of vaccine adopts a well tested technology platform that uses harmless virus called vector that is not the one to cause COVID-19. The virus is modified to be a recombinant nonreplicating one, also called replication incompetent or replication deficient. Examples include Sputnik V developed by Gamaleya of Russia and Janssen produced by Johnson and Johnson, Vaxzevria by Oxford-Astra Zeneca which is being produced by Serum Institute of India as Covishield. Covishield is made from a weakened version of a common cold virus called Adenovirus from chimpanzees to trigger immune response in human host. Meanwhile, the Janssen vaccine contains a recombinant and replication incompetent human Adenovirus, Ad26 vector that encodes a stabilized variant of the SARS-CoV-2 spike protein that causes an immune response. Adenovirus does not cause COVID-19. Instead, when injected, the vaccine produces SARS-CoV-2 protein in human cell and induces immune response.

Sputnik V also known as GamCOVID –Vac is the third kind of Covid19 vaccine besides COVAXIN and Covishield to be approved by the Drugs Controller General of India (DCGI) for immunisation of public during this ongoing pandemic. This vaccine technology uses two harmless human adenoviruses Ad26 and rAd5 for first and second dose respectively. These viruses act as vector to deliver genetic code for COVID -19 viral protein that induces the immune system to tackle future infections.

Benefits of COVID Vaccines

The above elucidation establishes that COVID-19 vaccine platforms based on inactivated virus Protein subunit, vector and DNA/RNA , either deliver or make our body to produce harmless spike proteins found on the surfaces of the COVID-19 virus. This in turn prompts the human body to produce antibodies against the virus, thereby providing immunity for future infection. The basket of COVID-19 vaccines validated by the World Health Organization (WHO) is expanding quite fast. All the vaccines are subjected to clinical trials to test their safety and effectiveness before they are approved for immunisation of the public by Drugs Controller General of India. Data on the long term benefits and side effects of the vaccines are being continuously monitored at the appropriate level.

The WHO has indicated that vaccine hesitancy as one of the biggest threat to global health. Vaccine hesitancy refers to a situation in which people with access to vaccines, refuse or delay vaccination. The WHO and Health authorities across the globe are urging the public to get vaccinated as vaccines are meant to prevent the onset of disease or to reduce the severity of the disease. Moreover it lowers the risk of contracting an infection and at same time reduces the likelihood of virus transmission.

COVID vaccines not only protect against the disease, but also reduce the chance of viral spreading. Natural immunity compounded by vaccine induced immunity results in an effective means to safeguard oneself against viral infections. Adding to that, vaccines can be innovated as and when new variants of the virus come to the fore. Thus, vaccines remain the best hope for ending the pandemic. Ultimately, to defeat COVID-19 an effective combination of three measures is required – maintain natural immunity, vaccination and effective public health measures.

(The author is Associate Professor, Department of Zoology, University of Delhi. E-mail: sanjukta_das_kmc@yahoo.com).

Views expressed are personal.