Covid-19 Oral Vaccine: What Trial Says About Its Efficacy

The oral vaccine candidate uses an adenovirus as a vector to express the spike protein of SARS-CoV-2, and elicits a robust antibody response in the blood.

An investigational Covid-19 vaccine designed to be taken orally not only protects the host, but also decreases the airborne spread of the virus to other close contact | Representational Image

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New Delhi: An investigational Covid-19 vaccine designed to be taken orally not only protects the host, but also decreases the airborne spread of the virus to other close contact, animal studies that mimic human exposures have found. 

In a new study, Stephanie N Langel, a researcher at Duke Health, which is a world-class academic and health care system, along with other her colleagues, has demonstrated the potential of a Covid-19 vaccine that works through the mucosal tissue to neutralise SARS-CoV-2, limiting infections and the spread of the active virus in airborne particles. 

The findings were recently published in the journal Science Translational Medicine. 

In a statement issued by Duke Health, Langel, the lead author of the study, said considering most of the world is underimmunized, the possibility that a vaccinated person with a breakthrough infection can spread Covid-19 to unimmunised family or community members poses a public health risk. Several children worldwide are underimmunized. Langel added that there would be a substantial benefit to develop vaccines that not only protect against disease, but also reduce transmission to unvaccinated people. 

What Does The Oral Vaccine Consist Of?

The team includes researchers from American vaccine development firm Vaxart, and New Mexico-based private contract research organisation Lovelace Biomedical Research Institute tested a vaccine candidate which uses an adenovirus as a vector to express the spike protein of SARS-CoV-2. Adenoviruses are common viruses which typically cause mild cold- or flu-like illness, and can affect people of all ages any time of the year. The human vaccine candidate which uses an adenovirus as a vector is designed to be taken as a pill. 

How Does The Oral Vaccine Work?

The oral vaccine showed a robust antibody response in the blood and lungs of hamsters, the study said. Exposure to high levels of SARS-CoV-2 prompted breakthrough infections in the animals. The researchers observed that the vaccinated hamsters were less symptomatic than non-vaccinated hamsters, and had lower amounts of infectious virus in the nose and lungs. As a result, they did not shed as much virus through normal airborne exposures. Viral shedding is the phenomenon in which infected individuals, who may not yet be experiencing any of the viral symptoms, are shedding viral particles while they perform normal daily activities such as talking, and eating, and even while exhaling. 

How Are Mucosal Immunisations Better Than Intramuscular Injections?

Langel said that mucosal immunisations, unlike vaccines injected intramuscularly, increase the production of immunoglobulin A (IgA) in the lungs. IgA is the immune system's first line of defence against pathogens. The mucosal ports of entry are then protected, making it less likely that those who are vaccinated will transmit infectious virus during a sneeze or cough. 

Langel said that the researchers' data demonstrate that mucosal immunisation is a viable strategy to decrease the spread of Covid-19 through airborne transmission. She explained that the study focuses on the original SARS-CoV-2 strain, and new studies will be designed to test the vaccine against Omicron variants. 

A study published last month stated that a new protein-based antiviral nasal spray developed by an international team of researchers is more effective than antibody treatments. The new protein therapies were designed computationally and refined in the laboratory. They fight against Covid-19 infection by interfering with the ability of SARS-CoV-2 to enter host cells. According to the study, the top protein of the nasal spray neutralised the virus with similar or greater potency than antibody treatments with Emergency Use Authorisation (EUA) status from the US Food and Drug Administration (FDA).