The development of the COVID-19 vaccines was nothing short of a triumph of modern medicine. However, the one weakness of the shots was the inability to stop the spread of the virus. St. Jude Children’s Research Hospital CEIRR (SJCEIRR) researchers from Washington University in St. Louis (WashU) may have found a way to combat this shortcoming by targeting the virus’s point of entry — the nose and mouth. The study evaluating this vaccine candidate was recently highlighted in a WashU Medicine article.
Why is targeting the nose and mouth so integral to preventing transmission? Viruses such as influenza virus, SARS-CoV-2, and respiratory syncytial virus (RSV) multiply rapidly in the nose, allowing them to spread from person to person within the first few days of exposure. Intramuscular vaccines generate a less potent immune response in the nose than in the bloodstream, leaving the nose and mouth vulnerable against fast-spreading viruses.
Although it seems that targeting the nose and mouth will limit viral reproduction more efficiently, gathering the evidence necessary to prove that mucosal vaccines reduce transmission is trickier than one would expect, underscoring the importance of animal models in biological research. To address this gap, Jacco Boon, Ph.D., Michael Diamond, M.D., Ph.D., and other researchers developed and validated a model that mimics community transmission of SARS-CoV-2 in hamsters, which was then used to assess the efficacy of mucosal vaccination on SARS-CoV-2 spread. The study compared hamsters vaccinated with a nasal COVID-19 vaccine to those vaccinated with an intramuscular COVID-19 vaccine—the vaccine approved for use in humans—to evaluate the impact of both vaccines on airborne infection and transmission.
The study showed that hamsters that were vaccinated with the nasal vaccine and went on to develop SARS-CoV-2 infections did not transmit the virus to vaccinated or unvaccinated hamsters. In direct contrast, when hamsters were given an intramuscular COVID-19 vaccine, spread of the virus still occurred. In summary nasal vaccination—but not intramuscular vaccination—broke the cycle of transmission in hamsters.
These results have immediate and direct implications as the world prepares for a possible avian flu epidemic. Currently the avian flu virus is causing an outbreak in dairy cows and could adapt to humans. An intramuscular vaccine for avian influenza already exists, but a team of researchers at WashU, that includes Dr. Boon and Dr. Diamond, are harnessing these results to work toward a nasal vaccine for avian influenza.
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Read the article in Science Advances: