New research at the Washington University School of Medicine (WU) in St. Louis is closing in on an effective vaccine against the coronavirus.

The researchers have developed a single-dose vaccine that’s deliverable via the nose and effective at preventing infection with SARS-CoV-2 in mice. The results warrant further research on primates and, eventually, humans, the team writes. If these tests are successful, this would be the only COVID-19 vaccine deliverable via the nose, not an injection.

A nose for vaccines

“We were happily surprised to see a strong immune response in the cells of the inner lining of the nose and upper airway—and a profound protection from infection with this virus,” said senior author Michael S. Diamond, MD, Ph.D.

“These mice were well protected from disease. And in some of the mice, we saw evidence of sterilizing immunity, where there is no sign of infection whatsoever after the mouse is challenged with the virus.”

The team says that the vaccine had a particularly strong effect in the nose and deeper respiratory tract of the mice. Since this area is where the virus first establishes its foothold, fighting it off here can prevent an infection altogether.

The vaccine was created by inserting the coronavirus’ distinct spike protein, the biochemical structure it uses to enter our cells, into another type of virus — an adenovirus, the class that causes the common cold. This adenovirus forms the base of the vaccine. It was further manipulated by the researchers to make it unable to cause any illness and then introduced into the nose. This way, our cells can interact with it and ‘see’ the spike protein, which enables our body to create an appropriate antibody, while being completely safe.

The team adds that they added two mutations to the spike protein to keep it stable in a specific shape, making it easier for our bodies to generate antibodies.

Still, the biggest news regarding this vaccine is the method of administration. Adenoviruses are often used as mediators in vaccines, for example in those for Ebola and tuberculosis, but they’re administered through injection. What few other vaccines we currently have that are administered via the nose use a weakened, live virus. This limits the cases where they can be administered, and also are likely to pose a greater risk, as the viruses can, at least in theory, replicate inside the host.

“The nose is a novel route, so our results are surprising and promising. It’s also important that a single dose produced such a robust immune response,” says co-senior author David T. Curiel, MD, Ph.D., the Distinguished Professor of Radiation Oncology at WU.

“Vaccines that require two doses for full protection are less effective because some people, for various reasons, never receive the second dose.”

So did it work? The team says yes. They compared the intranasal administration technique to that of an intramuscular injection. The injected one caused the mice to become resistant to pneumonia, but didn’t prevent a SARS-CoV-2 infection in the respiratory tract. In a human equivalent, this would make patients experience a less-severe form of COVID-19, but wouldn’t protect them against becoming infected or spreading the virus.

The intranasal vaccine, meanwhile, completely prevented infection in the upper and lower respiratory tract. In a human equivalent, this would completely prevent an infection from taking root, and would stop carriers from spreading the disease.

Naturally, we should temper our enthusiasm — the vaccine has only been tested on mice so far. Until more research can be done, especially using human participants, this vaccine is far from being confirmed as efficient.

The paper “A single-dose intranasal ChAd vaccine protects upper and lower respiratory tracts against SARS-CoV-2” has been published in the journal Cell.