United States: A recent study identified that, despite saving millions of lives, the COVID-19 vaccines have not been able to end the pandemic owing to one notable weakness: They haven’t been able to stop the spread of the virus.
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A study conducted by scientists at Washington University School of Medicine in St. Louis revealed that next-generation vaccines that target the virus’s points of entry, which are the nose and mouth, could potentially do what traditional vaccination shots couldn’t: contain the spread of respiratory infections and prevent transmission.
The scientists tested the nasal COVID-19 vaccine, which has already been approved in India and licensed to Ocugen for further development in the US.
Research conducted on infected hamsters reveals that after vaccination, they did not pass the virus on to others, breaking the cycle of transmissions.
On the other hand, the injected Covid shots could not prevent the spread of the virus.
According to Jacco Boon, PhD, the senior author and professor of medicine of molecular microbiology and pathology & immunology, “To prevent transmission, you need to keep the amount of virus in the upper airways low,” as medicine.wustl.edu reported.
The development of oral vaccines is challenging
According to the experts, viruses like the influenza virus, SARS-CoV-2, and RSV multiply quickly in the nose and thus rapidly spread to other persons after exposure.
Traditional shots generate immunity, which takes at least a week to build to full strength. However, it is less potent in the nose than in the bloodstream, rendering the nose much less protected against the rapidly multiplying deadly virus.
However, in principle, a vaccine sprayed or dropped into the nose or mouth can potentially limit viral reproduction and lower the chance of its transmission.
However, as experts note, proving the efficacy of the mucosal vaccine after gathering evidence is rather tricky. The animal transmission models are not established properly, and tracking person-to-person transmission is considered a complicated task, as the number and variety of encounters a typical person has on any given day are hard to track.
How was the current study conducted?
In the latest study, Boon and colleagues developed and validated a model for community transmission with the help of hamsters. They were hence used to measure the effect of mucosal vaccination on the spread of SARS-CoV-2, as medicine.wustl.edu reported.
The immunized groups of hamsters were inoculated with the nasal iNCOVACC used in India or injected with the Pfizer vaccine.
To compare, some of the hamsters were also rendered unvaccinated. After weeks, when their immunity responses were fully mature, the researchers infected the other hamsters with SARS-CoV-2 and then placed the immunized hamsters with the infected hamsters for eight hours.
This part of the experiment was similar to the experience of vaccinated people who are exposed to a person with COVID-19.
After eight hours, most of the vaccinated animals became infected. The virus was found to be present in the noses and lungs of 12 of 14 (86%) hamsters that had received the nasal vaccine, whereas 15 of 16 (94%) hamsters were in those receiving the injected vaccine.
The study showed that the hamsters taking nasal immunization had a virus level in their airways 100 to 100,000 times lower than those who had received the shot or had not been vaccinated.
In the second step of the experiment, the researchers took vaccinated hamsters, who subsequently developed infections. They placed them with healthy vaccinated and unvaccinated hamsters for eight hours to model virus transmission from a vaccinated person to others.
They saw that none of the hamsters who were exposed to nasally vaccinated hamsters got infected, notwithstanding whether the recipient hamster had been vaccinated or not.
On the other hand, almost half of the hamsters who were exposed to hamsters vaccinated by injection became infected – again, notwithstanding the immunization status of the recipients.
Thus, the study proved that the vaccination through the nose, but not by injection, could potentially break the cycle of transmission.
Boon said, “Mucosal vaccines are the future of vaccines for respiratory infections,” as medicine.wustl.edu reported.
“Historically, developing such vaccines has been challenging. There’s still so much we don’t know about the kind of immune response we need and how to elicit it. I think we’re going to see a lot of very exciting research in the next few years that could lead to big improvements in vaccines for respiratory infections,” he added.