Preliminary data released by Cadila Healthcare (Zydus Cadila) from animal trials show that their DNA-plasmid vaccine candidate ZyCoV-D has induced immune response in multiple animals. Apart from generating neutralising antibodies post vaccination, the vaccine candidate has also induced T-cell response, claimed the firm. (T cells are central players in the immune response to viral infection.)

Furthermore, the stability data showed that ZyCoV-D can be stored at 2 to 8 degrees Celsius for the long term and at 25 degrees Celsius for short term (a few months). The vaccine is in phase 3 clinical trials in India with over 30,000 people.

Being able to store and transport a vaccine at room temperature can ease several logistical challenges in taking the vaccine to the hinterland since it significantly reduces the cold chain requirements. “In the context of a pandemic outbreak, the stability profile of a vaccine plays a vital role in easy deployment and distribution for mass vaccination,” Zydus Cadila said.

In a research paper published in bioRxiv, Zydus claimed that the DNA plasmid manufacturing process is easily scalable with substantial yields.

The immunogenicity study for ZyCoV-D vaccine was carried out in mouse, guinea pig and New Zealand rabbit model. Two weeks after immunisation, the animals were given the first booster dose and then tests were performed to determine antibody titers in different animal sera samples.

ZyCoV-D was evaluated in different animal models and has “demonstrated ability to elicit immunogenic response against SARS-CoV-2, S-antigen in animal species,” the company noted. “Primary antibody response starts mounting in serum two weeks after two doses and reaches peak two weeks after third immunisation,” it added.

Zydus Cadila said that serum IgG antibody levels against spike antigen in mice were maintained even after three months after the last dose, suggesting a long-term immune response generated by the DNA vaccine candidate. “This also indicates that ZyCoV-D can possibly induce robust secondary anamnestic immune response upon re-exposure,” Zydus claimed.

Conventional vs DNA vaccine

Conventional active vaccines are made of a killed or weakened form of the infectious agent. DNA plasmid vaccine is a relatively new approach where a piece of DNA containing the genes for the antigens is injected. The body then learns to develop an immune response against the antigen, and when the actual pathogen attacks, the body is able to generate the specific antibodies against it.

DNA vaccines, Zydus claimed, have been shown to stimulate sustained immune responses.

Another advantage Zydus said was that the technology for producing the vaccine is very simple and rapid, and secondly the DNA molecule is stable, has a long shelf life, and does not require a strict cold chain for distribution.

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