The available COVID-19 vaccines have been called the biggest scientific accomplishment of the century and a modern miracle. But that hasn’t stopped scientists from working on making improvements. To that end, a new study presents promising data on a COVID-19 vaccine that is designed to be taken as a pill. Moreover, the vaccine not only protects the host, but also decreases the airborne spread of the virus to other close contacts.
The experiments, done in a hamster model that mimics human exposures, demonstrated the potential of a COVID vaccine that works through the mucosal tissue to neutralize the SARS-CoV-2 virus, limiting infections and the spread of active virus in airborne particles.
The findings are published in Science Translational Medicine in the paper, “Adenovirus type 5 SARS-CoV-2 vaccines delivered orally or intranasally reduced disease severity and transmission in a hamster model.”
“Considering most of the world is under-immunized—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,” said Stephanie Langel, PhD, medical instructor in the department of surgery, Duke University School of Medicine. “There would be a substantial benefit to develop vaccines that not only protect against disease, but also reduce transmission to unvaccinated people.”
Langel and colleagues—including teams from the vaccine developer Vaxart and the clinical research non-profit Lovelace Biomedical Research Institute—tested an orally-delivered adenovirus type 5-vectored SARS-CoV-2 vaccine candidate that expresses the spike protein.
Hamsters, vaccinated by the oral or intranasal route, had robust and cross-reactive antibody responses. 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, had lower amounts of infectious virus in the nose and lungs.
More specifically, the authors wrote, “Oral- or intranasal-vaccinated hamsters had decreased viral RNA and infectious virus in the nose and lungs and experienced less lung pathology compared to mock-vaccinated hamsters after SARS-CoV-2 challenge.”
The hamsters also did not shed as much virus through normal airborne exposures. The authors wrote that naïve hamsters, exposed in a unidirectional air flow chamber to mucosally-vaccinated, SARS-CoV-2-infected hamsters, also had lower nasal swab viral RNA and exhibited fewer clinical symptoms than control animals. This suggests that the mucosal-route reduced viral transmission.
Unlike vaccines that are injected into the muscle, Langel said, mucosal immunizations increase production of immunoglobulin A (IgA)—the immune system’s first line of defense 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.
The same platform encoding the SARS-CoV-2 spike and nucleocapsid proteins elicited mucosal cross-reactive SARS-CoV-2-specific IgA responses in a Phase I clinical trial (NCT04563702).
“Our data demonstrate that mucosal immunization is a viable strategy to decrease the spread of COVID through airborne transmission,” Langel said.