Injecting a vaccine against COVID-19, influenza or tuberculosis under the skin is actually not very logical when you look at it closely. The pathogens penetrate through the nose or mouth with the breathing air into the upper respiratory tract and later into the lungs. The vaccine injected under the skin is initially not effective where the infection that is to be warded off is taking place. However, this type of systemic vaccination has been working since 1796, when Edward Jenner vaccinated the first human against smallpox. But for respiratory diseases, another vaccination method might work better.
Immune training at the site of infection
The crux is that the vaccines that are injected under the skin cause a general immune reaction, but only poorly reach the immune cells that are waiting for pathogens in the mucous membranes of the respiratory tract. But it is precisely these cells that are responsible for fighting off the viruses and bacteria that we breathe. The strategy that numerous researchers around the world are pursuing is to let the immune training take place where the infection will later take place. They are developing intranasal vaccines that are sprayed onto the nasal mucosa as a nasal spray. With Fluenz Tetra from Astra Zeneca, a first intranasal attenuated live vaccine has arrived in practice – but it only works well in children and is only used up to the age of 18.
This setback in the broad effect for people of all ages – research has been going on for decades on intranasal flu vaccines, which can be used widely and would be very helpful, especially in areas with a weak medical infrastructure – has drawn vaccine research to a different strategy: aerosol vaccines that are inhaled like an allergy or asthma spray. For measles, tuberculosis and COVID-19, the first inhalation vaccines are already being tested in humans in early clinical trials. Direct comparisons have shown that tuberculosis vaccines are: The inhaled vaccines prepare the mucous membranes of the airways for attack by Mycobacterium tuberculosis – the injections do not.
We have been confronted with the corona virus and the pandemic for almost two years now. The large complex of topics provides a lot of material for reporting. Here is a selection of articles about new variants, symptoms such as Long Covid and news about the vaccines.
Researchers at McMaster University in Canada took a closer look at what happens when a vaccine is inhaled and how it differs from an intranasal vaccine. They used a tuberculosis vaccine and measured droplet distribution, immune response and efficacy in mice. The background: The only COVID-19 vaccine in a clinical study that can be inhaled also comes from the Canadian university. It is currently in phase 1, the first level of human testing, and is designed as a booster dose after two or three doses of injected mRNA vaccines.
Vaccine nasal sprays only reach the upper respiratory tract
The McMaster team has observed that vaccine nasal sprays primarily reach the nose and throat. In these upper zones of the respiratory tract, however, infections are rarely severe. Only when the viruses penetrate deeper into the lungs do people become seriously ill – but the intranasal vaccines cannot reach the deeper airways and therefore cannot protect them either.
Aerosol sprays, on the other hand, propel the droplets containing the vaccine deep into the lungs. The researchers have observed that significantly stronger immune responses to the vaccine then take place there than in the upper respiratory tract.
To decide whether inhaled vaccines are superior to intranasal vaccines only for tuberculosis vaccine or in general and future research should focus on them, they want to study the responses of the different mucous membranes in the nose and lungs to vaccines. They are looking for answers to the questions of how well these mucous membranes can absorb the vaccines, how strong the T-cell immunity triggered by the vaccination is and what protection this offers in the long term.