While standard vaccines administered via jabs into muscle tissue have been shown to protect against severe COVID-19, newer variants like Omicron can still be spread from infected, vaccinated individuals. Paper author and immunologist Dr Stephanie Langel of the Duke University School of Medicine explained: “Most of the world is under-immunised — and this is especially true of children. “The possibility that a vaccinated person with a breakthrough infection can spread Covid to unimmunized family or community members poses a public health risk. There would be a substantial benefit to develop vaccines that not only protect against disease but also reduce transmission to unvaccinated people.”
In their study, Dr Langel and colleagues experimented with a vaccine candidate that uses an adenovirus as a vector to express the spike protein that SARS-CoV-2 — the virus that causes COVID-19 — uses to gain access to cells.
Adenoviruses are a broad family of some 50 viruses known to cause a wide variety of illnesses from the common cold, conjunctivitis, gastroenteritis, and bladder infection to life-threatening multi-organ diseases in the clinically vulnerable.
The team developed both intranasal and oral formulations of their vaccine candidate and tested it on hamsters. An advantage of the latter is that it is easy to administer.
The experimental vaccine works through the mucosal tissues in the nose and lungs — helping to increase the production of immunoglobulin A, the immune system’s first line of defence against pathogens.
This helps to better protect the nose and lungs, thereby making it less likely that the recipient of the vaccine will transmit the virus via coughing or sneezing if infected.
The researchers determined that both delivery routes — oral and intranasal — induced strong antibody responses in the hamsters.
When infected with Covid, the previously vaccinated hamsters exhibited a reduced viral load and exhibited fewer signs of lung damage.
In a follow-up experiment, the team exposed unjabbed hamsters to their peers who had been both vaccinated, and then infected.
The team found that the unvaccinated hamsters exhibited both lower viral RNA levels and milder symptoms when infected via their vaccinated peers than those exposed to unvaccinated ones — indicating that the immunisation helped reduce transmission rates.
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Dr Langel cautioned, however, that the current study pitted the trial vaccine against the original SARS-CoV-2 virus.
Further research will therefore be required, she said, to test the efficacy of the vaccine against more recent variants like Omicron.
The research was funded in part by the Bill and Melinda Gates Foundation.
The full findings of the study were published in the journal Science Translational Medicine.