Nasal COVID-19 Vaccine Halts Transmission of SARS-CoV-2

A study by researchers at Washington University School of Medicine in St. Louis indicates next-generation vaccines that target a virus’s points of entry — the nose and mouth — may be able to contain the spread of respiratory infections and prevent transmission. Using a nasal COVID-19 vaccine based on Washington University technology, approved for use in India and licensed to Ocugen for further development in the U.S., the researchers showed that vaccinated hamsters that developed infections did not pass the virus on to others, breaking the cycle of transmission. In contrast, an approved COVID-19 vaccine that is injected failed to prevent the spread of the virus.

For the study, the researchers developed and validated a model for community transmission using hamsters and then used it to assess the effect of mucosal vaccination on the spread of SARS-CoV-2. (Unlike mice, hamsters are naturally susceptible to infection with SARS-CoV-2, making them the ideal laboratory animals for a transmission study.) The groups of hamsters were immunized with laboratory versions of approved COVID-19 vaccines: the nasal iNCOVACC used in India or the injected Pfizer vaccine. For comparison, some hamsters were not immunized. After giving the vaccinated hamsters a few weeks for their immune responses to fully mature, the researchers infected other hamsters with SARS-CoV-2 and then placed the immunized hamsters with the infected hamsters for eight hours. This first step of the experiment mimics the experience of vaccinated people who are exposed to a person with COVID-19.

After spending eight hours with infected hamsters, most of the vaccinated animals became infected. Virus was found in the noses and lungs of 12 of 14 (86 percent) hamsters that had received the nasal vaccine, and 15 of 16 (94 percent) hamsters that had received the injected vaccine. Importantly, while most animals in both groups were infected, they weren’t infected to the same degree. Hamsters that had been nasally immunized had virus levels in the airways 100 to 100,000 times lower than those that had received the shot or had not been vaccinated. The study did not assess the animals’ health, but previous studies have shown that both vaccines reduce the likelihood of severe illness and death from COVID-19.

In the second step of the experiment, the researchers took vaccinated hamsters that subsequently developed infections and placed them with healthy vaccinated and unvaccinated hamsters for eight hours to model transmission of virus from a vaccinated person to others. None of the hamsters that were exposed to nasally vaccinated hamsters became infected, regardless of whether the recipient hamster had been vaccinated or not. In contrast, roughly half of the hamsters that were exposed to hamsters vaccinated by injection became infected — again, regardless of the recipient’s immunization status. In other words, vaccination through the nose — but not by injection — broke the cycle of transmission.

According to senior author Jacco Boon, PhD, a professor of medicine, molecular microbiology and pathology and immunology, this could be important as the world prepares for the possibility that avian influenza, currently causing an outbreak in dairy cows, might adapt to humans and trigger a flu epidemic. An injectable vaccine for avian influenza already exists, and a team of researchers at Washington University is working toward a nasal vaccine for avian influenza.