Scientists have shown that a single-dose COVID-19 vaccine candidate that could potentially be stored at room temperature can induce immunity to coronavirus in mice.
The vaccine described in the ACS Central Science Journal contains ultra-small nanoparticles that are occupied with the spike proteins of the coronavirus and enable entry into host cells.
“Our goal is to make a single vaccine that doesn’t require a cold chain to be stored or transported. If we’re doing well, it should be cheap too,” said study co-author Peter Kim of Stanford University in the United States.
“The target audience for our vaccine are low and middle income countries,” added Kim.
According to the researchers, virus-based vaccines that use viruses to deliver immunizing proteins are often more effective than those that contain only isolated protein portions of a virus.
They said nanoparticle vaccines balance the effectiveness of virus-based vaccines with the safety and ease of manufacture of protein vaccines.
To develop the vaccine, the scientists first removed a section near the bottom of the coronavirus spike protein and combined it with ferritin nanoparticles – an iron-containing protein – previously tested in humans.
In the following tests on mice, the researchers compared their truncated spike nanoparticles to four other possible variations – full spiked nanoparticles, full spikes, or partial spikes with no nanoparticles, and a vaccine containing only the portion of the spike that is attached to cells during infection binds.
Scientists then tested the effectiveness of these vaccines against a safer pseudo-coronavirus that was modified to carry the spike proteins.
They determined the potential effectiveness of each vaccine by monitoring the levels of virus-neutralizing antibodies produced in the mice’s immune systems.
After a single dose, the study found that two nanoparticle vaccine candidates resulted in neutralization of antibody levels that were at least twice as high as in people with COVID-19.
According to the scientists, the shortened spike nanoparticle vaccine produced a significantly higher neutralization response than either the binding spike or the full spike vaccine.
After a second dose, they said that mice that received the shortened spike nanoparticle vaccine had the highest levels of neutralizing antibodies.
Based on the results, Stanford scientists said their nanoparticle vaccine could induce COVID-19 immunity after just one dose.
Scientists believe the vaccine could also be stored at room temperature and are currently looking into whether it can be shipped and stored in freeze-dried powder form.
“This is a very early stage and there is still a lot to be done,” said Abigail Powell, lead author of the study.
Researchers hope to improve the nanoparticle vaccine candidate to bring it closer to early human clinical trials.