The Science Behind Covid-19 Vaccines Approved by India

Zydus Cadila may soon seek emergency use authorization (EUA) for its DNA-plasmid technology-based Covid-19 vaccine from the Drug Controller General of India. If approved, this would be the world’s first DNA-plasmid vaccine.

Since the company has already conducted trials on age groups 12-18, this could also be India’s first vaccine for children. Even as experts say that the children rarely develop severe forms of Covid-19, the states of Karnataka and Maharashtra have recently witnessed a spike in paediatric Covid cases, and some deaths too. Not only instances of coronavirus, but cases of paediatric black fungus were also reported in the past two months.

After the second wave wreaked havoc across India, Experts believe that vaccines are the best way forward for India, which launched its mass inoculation program in January. Since then, official data showed that only 11% of the population has received at least one vaccine dose while just 3.4% have completed the required two doses. While India’s urban population that bore the brunt of overwhelmed health infrastructure during the second wave has been actively getting jabs but the authorities face a serious challenge in inoculating its rural population.

However, some studies, including lab-based work and analysis of real-world data, have suggested current Covid vaccines are somewhat less effective against the Delta variant than the Alpha variant. The experts also claim that the “vaccines protect, and a second dose is very important against the Delta variant”, reported The Guardian.

Zydus: ZyCov-D is a ‘plasmid DNA’ vaccine that falls under the category of ‘nucleic acid’ vaccines. It has established a DNA vaccine platform that uses a non-replicating plasmid, which carries the “gene of interest”. It means that the DNA sequence inserted will match the sequence pattern of the virus, pushing the body to build antibodies against it.

The platform can be manufactured easily as it requires minimal biosafety requirements (BSL-1) unlike attenuated vaccines which require the top BSL-3 or BSL-4 units. It is also known to have lower cold chain requirements, making the distribution easier.

Bharat Biotech partnered with the National Institute of Virology (NIV) and the Indian Council of Medical Research (ICMR) for the ‘inactivated coronavirus’ vaccine Covaxin. Trial results have shown the vaccine has an efficacy of 78 per cent. Pathogens (viruses or bacteria) that cannot multiply can be injected into the arm without causing covid-19 inside the body. Using chemicals like formalin, the vaccine works by teaching the immune system to make antibodies against the SARS-CoV-2 coronavirus.

The inactivated viruses are then mixed with a tiny amount of an aluminum-based compound called an adjuvant which stimulates the immune system to boost its response to a vaccine. At Least 55 crore doses of Covaxin would be available by December, the government said.

The University of Oxford partnered with the British-Swedish company AstraZeneca developed a vaccine based on the ‘viral-vectored platform.’ The Serum Institute of India is manufacturing the vaccine known as Covishield in India. Viral vector-based vaccines don’t actually contain antigens but rather use the body’s own cells to produce them. It uses a modified virus (the vector) to deliver genetic code for antigen in the case of COVID-19 spike proteins found on the surface of the virus, into human cells.

The coronavirus spike protein gene is added to two types of adenovirus, one called Ad26 and one called Ad5, to enable them to invade cells but not replicate. Once infected, the cells make large amounts of antigen, triggering an immune response against the virus. The Oxford-AstraZeneca vaccine uses a chimpanzee adenovirus because humans will not have pre-existing antibodies to this adenovirus. Over 75 crore doses will be made available by the SII between August and December.

Sputnik V:
Russian Ministry of Health’s Gamaleya Research Institute developed a ‘non-replicating viral vector’ coronavirus vaccine Sputnik V. The two-dose vaccine has an efficacy rate of 91.6 per cent. Sputnik V uses two human adenoviruses Ad5 and Ad26, the adenoviruses bump into cells and latch onto proteins on their surface. Once injected into the body, these vaccine viruses begin infecting our cells and inserting their genetic material – including the antigen gene – into the cells’ nuclei. Human cells manufacture the antigen as if it were one of their own proteins. At least 15.6 crore doses will be available in India by December.

(Source: News 18)