Could Plants Make Vaccines Cheaper, Easier to Store and Simpler to Deliver?

The next big leap in vaccine access could come from plants engineered to produce vaccine proteins that are cheaper to manufacture, easier to store and, in some cases, potentially delivered by mouth rather than injection.

A new review, "Plant-Produced Vaccines for Protection from Human and Veterinary Coronaviruses," examines this possibility. The paper, authored by Erin Egelkrout of the Applied Biotechnology Institute and published in the journal Vaccines, covers more than two decades of work in tobacco, maize, rice and other plants, arguing that the science has moved well beyond proof-of-concept, but commercialization remains the real test.

Plant Vaccines Have Already Proven They Can Work

The most important point in the review is that plant-produced vaccines are not merely speculative. Multiple coronavirus vaccine candidates have advanced into animal studies and human clinical trials, while one, Medicago's tobacco-produced COVID-19 vaccine, reached regulatory approval in Canada.

Clinical evidence from the Medicago programme was substantial. In a trial involving about 24,242 adults, the vaccine showed 69.5% efficacy against symptomatic COVID-19 and 78.8% efficacy against moderate-to-severe disease. Earlier studies also reported strong immune responses and persistence of neutralizing antibodies months after vaccination.

However, the programme also illustrates the distance between scientific success and commercial survival. Medicago struggled with production scale-up, changing vaccine demand and controversy surrounding its tobacco-industry ownership. The company ultimately closed and its vaccine was discontinued, despite having demonstrated clinical efficacy.

The challenge now is whether governments, investors and manufacturers can build regulatory, financing and production systems capable of carrying promising platforms through the expensive transition from laboratory validation to commercial deployment.

Maize Could Change the Economics of Vaccine Delivery

Among the platforms reviewed, maize stands out because it offers a different model of manufacturing and delivery. Vaccine proteins can be produced inside grain, where they may remain stable for long periods and potentially be processed into an orally administered form. Conventional vaccination depends on more than the vaccine itself. Cold storage, syringes, trained health workers and organized distribution networks all add costs and complexity. In low-resource or remote settings, these delivery requirements can become as important as the price of producing the antigen.

The review argues that maize-based production could help reduce some of those constraints. Recombinant proteins can be stored within seed, potentially reducing refrigeration requirements and allowing oral administration through processed material. The platform is also compatible with large-scale agricultural production, creating theoretical scope for rapid expansion.

The paper presents illustrative calculations suggesting exceptionally large production capacity and much lower raw-material costs for maize compared with tobacco. Those estimates are theoretical and depend on assumptions about protein expression, recovery and dosage, so they should not be read as demonstrated commercial costs. But they highlight why plant-based manufacturing attracts interest for pandemic preparedness and resource-constrained settings.

Vaccine innovation has often focused on speed of discovery, but equitable access also depends on how easily a product can be manufactured, stored and administered. A vaccine that tolerates heat and does not require injection could solve distribution problems that remain stubborn even after the science is finished.

Veterinary Vaccines May Reach Practical Use Faster Than Human Products

The case for plant-produced vaccines extends beyond human health. Coronaviruses also affect livestock, including pigs and poultry, where vaccination can be costly and labour-intensive when animals must be injected individually.

The review describes maize-produced vaccine candidates against transmissible gastroenteritis virus in pigs that reduced symptoms after oral administration and triggered neutralizing antibodies. Vaccinating breeding animals also increased antibody levels in serum, colostrum and milk, offering a potential pathway for transferring protection to young animals.

Other plant systems have also shown promising results in veterinary applications. A duckweed-produced vaccine candidate against avian infectious bronchitis virus generated systemic and mucosal immune responses in chickens and achieved complete protection in an experimental challenge.

Livestock vaccination operates under different commercial conditions from human medicine. Oral vaccines incorporated into feed could reduce labour costs, simplify administration and improve coverage across large herds or flocks, potentially making veterinary markets an earlier route to commercial adoption.

There is also a wider development implication. Better control of animal disease can protect farmer incomes, livestock productivity and food supply. In that sense, plant-produced vaccines sit at the intersection of public health, agricultural resilience and the broader One Health agenda linking human and animal disease risks.

The Biggest Barriers Are Now Funding, Regulation and Trust

Technical feasibility is no longer the main obstacle, the review concludes. Plant systems can produce vaccine antigens capable of triggering strong immune responses, but relatively few products have crossed the final bridge into routine commercial use.

Part of the problem is financial. Many candidates reach strong preclinical results but struggle to secure the capital needed for human trials and manufacturing scale-up. Large pharmaceutical companies may be reluctant to invest in unfamiliar production systems before extensive safety and efficacy data already exist, creating a financing gap precisely when development becomes most expensive.

Regulation and public perception add further complications. Plant-produced pharmaceuticals can raise questions about genetically modified organisms, containment and intellectual property. Tobacco platforms also require purification from unwanted compounds, while edible crops create their own regulatory concerns over separation from conventional food and feed systems.

The evidence base itself requires caution. The review is broad rather than systematic, drawing together studies conducted over more than two decades using very different plant species, vaccine designs, doses and animal models. It therefore cannot establish that one platform is definitively superior to another, even though maize appears particularly attractive for oral delivery and scale-up.

The potential advantages, lower storage requirements, simpler administration and large-scale production,are substantial, but they remain partly prospective. More human trials, comparative manufacturing studies and real-world cost analyses are needed before plant-grown vaccines can be treated as a proven solution to vaccine inequity.

Regardless, the strategic opportunity can't be dismissed. COVID-19 showed that the world can develop vaccines at extraordinary speed when urgency and financing align. The next challenge is making those vaccines easier to manufacture and easier to deliver, especially where health infrastructure is weakest.