COVID-19 vaccines were developed quickly and saved millions of lives, but they couldn’t completely stop the virus from spreading.
A new study with hamsters suggests that vaccines targeting the nose and mouth might be the solution.
While traditional COVID-19 vaccines reduced illness and death, they didn’t prevent people from spreading the virus.
The new research shows that next-generation vaccines aimed at the nose and mouth could stop respiratory infections like COVID-19 and flu from spreading.
The study used a nasal COVID-19 vaccine approved in India and being further developed in the US.
Researchers found that hamsters vaccinated through their noses didn’t pass the virus to others, breaking the chain of transmission. In contrast, hamsters given a regular injected vaccine still spread the virus.
Published in Science Advances, the findings suggest that mucosal vaccines, which are sprayed into the nose or dropped into the mouth, may be more effective than shots. These vaccines can better control virus levels in the upper airways, reducing the chance of transmission.
“To stop the virus from spreading, you need to keep the amount of virus in the nose low,” says Jacco Boon, a senior researcher at Washington University School of Medicine. “If there’s less virus in the nose, you’re less likely to infect others through coughing, sneezing, or even breathing.”
Developing nasal vaccines is challenging because viruses like COVID-19 and flu multiply quickly in the nose and spread fast. Traditional vaccines generate an immune response that takes time to build up and is weaker in the nose compared to the bloodstream. This leaves the nose vulnerable to fast-spreading viruses.
A nasal or oral vaccine can limit virus reproduction and transmission by creating an immune response right where it’s needed. However, proving that these vaccines reduce transmission has been difficult due to the complexity of tracking virus spread among people.
In this study, Boon and his team developed a model using hamsters to study community transmission. They vaccinated groups of hamsters with either the nasal iNCOVACC vaccine used in India or the injected Pfizer vaccine. Some hamsters were left unvaccinated for comparison. After allowing time for the immune responses to develop, the researchers exposed the vaccinated hamsters to others infected with SARS-CoV-2, the virus causing COVID-19.
Most of the vaccinated hamsters got infected, but those with the nasal vaccine had 100 to 100,000 times lower virus levels in their airways compared to those with the injected vaccine or no vaccine at all.
In the second part of the experiment, researchers tested whether vaccinated hamsters could spread the virus to others. They found that none of the hamsters exposed to nasally vaccinated hamsters got infected. In contrast, about half of those exposed to injected-vaccine hamsters did get infected. This shows that nasal vaccination can break the transmission cycle.
These findings could be crucial for future epidemics, such as a potential avian flu outbreak. While an injectable avian flu vaccine already exists, researchers are working on a nasal version. Boon believes mucosal vaccines represent the future of respiratory infection control, though more research is needed to understand the best ways to develop them.
“Mucosal vaccines are the future of vaccines for respiratory infections,” Boon says. “There’s still much to learn about the immune response needed and how to create it. We can expect exciting advancements in vaccine research in the coming years.”
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