Imagine inhaling only a few drops of liquid or mist to protect yourself from COVID-19. This is the idea behind COVID-19 nasal vaccines, and they have recently been getting a lot of attention as an aerosol or liquid. These nasal vaccines would be based on the same technology as normal injection vaccines. But as Mayuresh Abhyankar, a researcher at the University of Virginia who studies infectious diseases and works on nasal vaccines, explains, vaccinating someone right where the coronavirus is likely to start its attack has many immune benefits.
1. What are nasal vaccines?
Nasal vaccines are given, as the name implies, by the nose. More accurately called intranasal vaccines, these vaccines are liquids that can be given as a spray or by a dropper or syringe.
The most common nasal vaccine is FluMist, a nasal spray that uses inactivated flu virus to protect against the flu. An intranasal vaccine could be a weakened live virus similar to FluMist, a nucleic acid vaccine such as mRNA coronavirus vaccines, or a protein vaccine such as hepatitis B vaccines or the CorbeVax coronavirus vaccine.
Intranasal vaccines are best suited to protect against nasal pathogens, such as the flu or coronavirus. By mimicking the first step of natural exposure to a pathogen in the air, these vaccines help train a person’s immune system at the potential site of infection.
Scientists have shown that the first immune response to the airways after a person is exposed to a virus in the air can influence a person’s degree of illness. Thus, in theory, intranasal vaccines could provide better protection than vaccines given by arm injection.
2. How does coronavirus infect people?
SARS-CoV-2, the virus that causes COVID-19, usually enters the body through the nose and lands on the mucous membrane at the back of the nasal passage and throat. The virus then enters the cells it touches, replicates and spreads.
Just below these mucous membrane cells are many types of immune cells that make up what is called the mucosal immune system. Mucosal immune system cells are the first to identify invasive coronavirus particles and begin to assemble a protective response.
In an unvaccinated individual, these immune cells take about two weeks to generate a protective response after encountering the coronavirus. At this point, the virus may have easily infected other parts of the body, such as the lungs, which can lead to serious illness.
Nasal vaccines follow many of the same steps. When you inhale a nasal vaccine, the particles land on the mucous membrane of the nasal cavity or the back of the throat, enter the cells in these places and trigger an immune response. This process teaches the body the coronavirus and allows it to deal with any future real infection.
3. How do nasal and intramuscular vaccines differ?
When you receive a COVID-19 vaccine in your arm, the vaccine triggers a strong immune response in the cells near where you received the vaccine. It also causes your immune system to produce specific antibodies to coronavirus and other immune cells in other parts of your body.
When the coronavirus begins to infect a person’s respiratory tract cells, nearby immune cells will begin to build up a defense. Your body will also send antiviral immune cells and antibodies from other places to the site of infection. But when enough coronavirus-specific immune cells cluster around the site of infection to prevent the virus from replicating, it is likely that the virus has already begun to spread throughout the body, making it difficult for the virus to spread. keep your immune system up to date.
Nasal vaccines mimic the virus in order to prepare the immune system against a virus, just like any other vaccine. But most importantly, they also mimic the process of infection and increase the protective response within the immune system of the mucous membrane of the nose and throat. In simple terms, intranasal vaccines are like knowing that there will be an intrusion and putting the guards in the right place before the problems start.
Science confirms this idea. In a face-to-face comparison, AstraZeneca’s AZN,
The COVID-19 vaccine provided greater protection for intranasally vaccinated hamsters compared to intramuscularly vaccinated hamsters.
Nasal vaccination could also be used in conjunction with intramuscular immunization. In a recent study, my colleagues and I gave some mice a nasal and intramuscular vaccine and exposed them to a lethal dose of SARS-CoV-2: 100% of these mixed vaccinated mice survived, in compared to only 10% of the unvaccinated. mice.
We are now testing whether this mixed approach is superior only to intranasal or intramuscular only approaches.
Finally, intranasal vaccines are painless, non-invasive and do not require specialized training to use.
4. What are the risks of nasal vaccines?
Getting the right dose can be more difficult with nasal vaccines than with an injection, especially with young children. If someone has their nose covered or sneezes part of the vaccine before it is completely absorbed, this may result in a lower dose than desired.
There are also some unique health risks. All vaccines go through safety testing and rigorous clinical trials, but these processes are especially important for nasal vaccines for the simple fact that the nose is close to the brain. In 2000, 27.7% of people who received an inactivated flu vaccine in Switzerland developed transient facial paralysis, also known as Bell’s palsy. Researchers later found that a bacterial toxin added to the vaccine to improve the immune response was to blame.
This is the only reported case of neurological problems resulting from intranasal vaccines, but it is something to keep in mind.
5. How long does it take for intranasal vaccines against COVID-19 to be ready?
At the end of May 2022, there are no COVID-19 intranasal vaccines approved for human use. There are currently seven in clinical trials, and three of them, manufactured by Beijing Wantai Biological Pharmacy 603392,
Bharat Biotech and Codagenix and Serum Institute of India are in phase 3 human trials.
In the coming months, the results of these trials will not only show the safety of these promising new vaccines, but also whether they perform better than the vaccines currently in use.
Mayuresh Abhyankar is an Associate Professor of Infectious Diseases and International Health at the University of Virginia in Charlottesville. This was first published by The Conversation: “Nasal vaccines against COVID-19 help the body prepare for infection right where it starts: in the nose and throat.”