The study led by Duke University researchers demonstrated the potential of a Covid vaccine that works through the mucosal tissue to neutralise the SARS-CoV-2 virus, limiting infections and the spread of active virus in airborne particles.
“Considering 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 unimmunised family or community members poses a public health risk,” said Stephanie N. Langel, doctoral researcher at varsity.
“There would be a substantial benefit to develop vaccines that not only protect against disease, but also reduce transmission to unvaccinated people,” Langel added.
The findings are published in the journal Science Translational Medicine.
Langel and team — including teams from the vaccine developer, Vaxart and a clinical research non-profit Lovelace Biomedical Research Institute — tested a vaccine candidate that uses an adenovirus as a vector to express the spike protein of the SARS-CoV-2 virus. The human vaccine is designed to be taken as a pill.
In studies using hamsters, the vaccine elicited a robust antibody response in blood and the lungs.
When the animals were exposed to the SARS-CoV-2 virus at high levels, prompting breakthrough infections, they were less symptomatic than non-vaccinated hamsters, and had lower amounts of infectious virus in the nose and lungs. Because of this, they did not shed as much virus through normal airborne exposures.
Unlike vaccines that are injected into the muscle, Langel said, mucosal immunisations increase production of immunoglobulin A (IgA) — the immune system’s first line of defence against pathogens — in the nose and lungs.
These 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.
“Our data demonstrate that mucosal immunisation is a viable strategy to decrease the spread of Covid through airborne transmission,” Langel said.
Langel said the study focused on the original SARS-CoV-2 virus, and new studies will be designed to test the vaccine against Omicron variants.