Mid-November, when the WHO released its draft landscape report of Covid-19 vaccines, it listed a total of 212 candidates that are at various stages of development.

While 48 of these vaccines have reached clinical evaluation, 168 are listed as being in the pre-clinical phase. At the very bottom of the former list is a unique candidate that is using plant-based bio-engineering methods to develop its solution.

Under development by Canadian firm Medicago Inc, the vaccine has reached the second phase of clinical trials. The WHO list includes three more plant-based vaccines that are, however, in the pre-clinical stage.

Tapping plants

In traditional methods of vaccine production, the virus is injected into fertilised chicken eggs or organisms such as bacteria or yeast. Allowing the virus to replicate for a few days, the viral particles are then isolated and used to make the vaccine. Synthetic vaccines use no organisms at all and are totally developed in a test tube.

Plant-based biotechnology, on the other hand, harnesses the speed, flexibility and efficiency of plants to come up with vaccine candidates. Rather than replicate a virus, it aims to engineer a virus-like protein (VLP) in living plants. A VLP is a non-infectious version of a given virus. Medicago used a type of tobacco plant for the purpose.

When administered, a VLP mimics a virus and is recognised by the immune system, thus eliciting a protective response.

Since it lacks a genome, it is seen as completely harmless during human trials. Medicago claimed a 100 per cent success rate in Phase 1 of its clinical evaluation.

However, a VLP alone cannot be used to produce a quick vaccine for human use, especially in pandemic situations where there is demand for a swift solution. For this purpose, Medicago’s candidate is added with adjuvants from Glaxo Smith-Kline (GSK) and Dynavax.

An adjuvant enhances the immune response to viruses, thereby creating a stronger and longer lasting immunity against infections than can be achieved by the vaccine alone. GSK’s adjuvant technology is used by several organisations that are in the race to develop a Covid-19 vaccine.

Quicker process

Compared to traditional methods, which usually take up to six months before a vaccine candidate is identified, the living plant technology is quicker. According to Medicago, it successfully produced a VLP of the coronavirus in early March 2020, just 20 days after obtaining a SARS-CoV-2 strand for research.

Medicago says it produces research grade Covid-19 vaccine doses in just 19 days and clinical grade doses in 6-8 weeks. Back in 2012, in the wake of the H1N1 pandemic, it supplied 10 million of research grade doses in one month, the company claims.

Using plants as bio-factories has several advantages. They can be produced cheaply in very high amounts and carrier plants such as potatoes and corn are readily accepted by patients and antigens derived can be stored for long periods of time.

All the leverage the technology provides may not mean that it can lift more than its weight in the fight against Covid. Having found increasing acceptance only during the past three decades, the capacities needed to cater to global demand for Covid vaccine may be out of its reach. In these times, when unprecedented collaboration is seen among the scientific community to fight Covid-19, plant-based biotechnology might just hope to move up a step in the world of vaccines.

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