Analysis of the efficacy of a plant-based vaccine for COVID-19

Aakancha Shaw, St. Xavier’s College, Kolkata

We are all well aware of the increasing number of deaths due to the COVID-19 pandemic. With over 3.42 million deaths recorded, the pandemic continues to impose risk on both the economic as well as healthcare sectors. COVID-19 or coronavirus is caused by SARS-CoV-2, which is an enveloped virus and is known to share more than 50% similarity of sequences with other dangerous members of the human coronavirus family-like SARS-CoV-1 and MERS (the Middle East Respiratory Syndrome Coronavirus). Although the efforts for developing potent vaccines cannot be neglected, yet concerns remain about the effectiveness of these vaccines against the newly emerging mutants of the virus. Some of these mutants may have higher virulence and infectivity, so such vaccines are desirable which can successfully resist the virus and negate the immune evading ability of SARS-CoV-2. It has become very important to modify the existing vaccines or to develop new potent vaccines to make them more appropriate for the novel mutants. 

The plant-based vaccine

A Canadian biotechnology company named Medicago developed a SARS-CoV-2 vaccine candidate for the scientists to investigate the immunogenicity and safety profile of the virus. The plant-based vaccine candidate consisted of a self-assembling COVID-19 like particle that displays trimmers of recombinant SARS-CoV-2  spike protein that was embedded into the lipid bilayer of nano-particles. The particles(virus-like) closely resembled the native structure of SARS-CoV-2 and are produced in the plant Nicotiana benthamiana (colloquially known as benthi). To improve the efficiency of the vaccine, the oil in water adjuvant system 03 was used.  After immunization, the adjuvant was seen to trigger a transient innate immune response in peripheral blood which in turn strengthened the induction of cellular adaptive and humoral immune responses to the vaccine antigen. 

The above image shows plants of the Nicotiana genus. (The vaccine being talked about in this article is Nicotiana-based)

Experimental study results on vaccine administration:

The experimental study was conducted on around 305 adults who were aged between 18 to 64 years and around 282 elderly people who were aged 65 years and above. At an interval of 21 days, the participants of the study were administered the two doses of the candidate vaccine. 

The immunogenicity, safety, and tolerability of the vaccine were assessed in the study. The immunogenic efficacy was determined based on the neutralizing responses of antibody and IL-4 (interleukin-4) related cellular immune responses. The tolerability of the vaccine in both the populations was quite good but mild reactogenicity was observed among the adults who were aged 65 and above. After the first vaccine dose local adverse events ( fatigue and muscle aches)  were observed in 94% of adults while after the second dose, 38% of the adults reported adverse events. In the case of older adults, 61% reported adverse events after the first dose while 55% people reported local adverse events after the second dose. The most common symptoms of these events were muscle pain and fatigue. The adverse events were mostly mild or moderate in intensity and the symptoms subsided between 1- 3 days. Also, none of the participants were seen to show any sign of vaccine-associated enhanced disease like anaphylaxis or some other potential immune disorders. 

This experiment showed that when compared to placebo-treated control participants around 45% of vaccinated adults and 30% of vaccinated older adults, showed an approximately 4-fold increase in the neutralization of antibody response after 21 days of the first dose. The study findings were quite significant and revealed that the candidate vaccine with adjuvant system 03 is quite well-tolerated in humans and 2 dose regimen of the vaccine is potential enough to induce robust antibody-mediated immune responses among individuals between 18-80 years. However, the report provided is solely based on phase 2 clinical trials of the vaccine. Thus, more phase trials are yet to be conducted before the vaccine receives approval for public usage. 

Also read: 3D Bioprinting: A Technology for Prevention and Therapy of Infectious Diseases

Reference:

1. Gobeil P, Pillet S, Séguin A, Boulay I, Mahmood A, Vinh D.C, Charland N, Boutet P, Roman F, Van Der Most R, Perez M.A.C, Ward B.J, Landry N. (2021). Interim Report of Phase 2 Randomized Trial of a Plant-Produced Virus-Like Particle Vaccine for Covid-19 in Healthy Adults Aged 18-64 and Older Adults Aged 65 and Older. medRxiv 2021.05.14.21257248; DOI: https://doi.org/10.1101/2021.05.14.21257248
2. Plant-produced COVID-19 vaccine shows potent immunogenic profile in humans: https://www.news-medical.net/news/20210520/Plant-produced-COVID-19-vaccine-shows-potent-immunogenic-profile-in-humans.aspx

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