So-called mucosal vaccines can be a response to long-term immunization.
As the pandemic continues, many countries are launching their recall shots. In the UK, the autumn recall campaign offers a fourth dose for people most at risk of contracting covid, including those with pre-existing conditions and those over the age of 50.
The fall booster shots are bivalent vaccineswhich means they focus on the original strain of SARS-CoV-2 (the virus that causes covid-19) and the omicron variant.
These vaccines are effective in recharging and boosting our immunity. But, as seen with the original covid vaccines, the protection they provide, especially against infections, is expected to diminish months later.
So consider a vaccination strategy that provides a long-term immunization. A new type – mucosal vaccines – could show promise on this front.
Mucosal vaccines are applied in the nose or throat via inhalable formulations. It may sound like something new, but we’ve actually been using them for years to vaccinate against diseases like the flu.
While traditional hypodermic injection vaccines produce a more systemic immune response, mucosal vaccines do something different. Viruses such as SARS-CoV-2 enter our system through the nose or mouth when we inhale small droplets that contain the virus. This means that immunity in the nose, mouth or throat are very important in stopping infections.
Mucosal vaccines are designed to act on this “mucosal immune system”. The mucosal immune system has the potential to stop the virus from entering the body, so scientists predict that mucosal vaccines could prevent infection.
Inhalable vaccines are absorbed through the mucous membrane of the nose, mouth or throat.
Mucosal immunity may also be better for our immune system to remember SARS-CoV-2. Memory lymphocytes are long-lived immune cells that remember the virus and carry instructions so they can be deployed quickly in the face of an attack. Systemic vaccines are not as effective at activating memory lymphocytes in the nose or throat, but mucosal vaccines are.
On the other hand, the fact that mucosal vaccines act locally implies this a smaller dose would be needed. This, combined with less stringent conservation measures than traditional vaccines, could allow them to be implemented much more efficiently in low-income countries and become an important tool for vaccine fairness.
Mucosal vaccines may also be more tempting for someone with a needle phobia. About 26% of the UK population admits to being afraid of needles, with the highest rates of phobia among young black and Asian groups – the demographics we know are reluctant to get vaccinated and vaccinated less.
A high percentage of the population has a phobia of hypodermic needles.
Obvious benefits, but what does the evidence say?
Several candidates for mucosal vaccines are being studied in preclinical and clinical studies. Recently published results from a nasal booster vaccine tested on mice showed it was there robust mucosal immune responses in the nasal and upper respiratory tract.
Similarly optimistic results have been reported in macaques and hamsters. Several tests are underway to see if these results can be repeated in humans.
Iran, Russia, India and China have already introduced mucosal vaccines although published data on their candidate vaccines remains scarce. Although some data has been published.
The results of a Phase II human trial of an inhalable vaccine, now being launched in China, have been revealed in a study that has not yet been peer-reviewed. Although the study did not evaluate mucosal responses, it did showed that systemic antibody levels were higher and remained higher throughout the six-month evaluation compared to a traditional brace.
China is one of several countries that have introduced the nasal vaccination system.
But it is an ambiguous picture. A phase I nasal formulation of the Oxford-AstraZeneca vaccine showed little or no initiation of the mucosal immune response and weaker systemic antibodies than the traditional vaccine.
The reason for these disparities is unclear, but it could be due to the method of application. Delivery of the mucosal vaccine requires precise aerosol science and engineering to ensure that the droplets containing the vaccine are easily inhaled.
Various strategies have been used in the administration of mucous vaccines, including nebulizers (a machine that turns liquids into a fine mist that can be inhaled), nasal sprays, and devices such as inhalers commonly used by asthmatics.
The size of the particles, the formulation (the ingredients and how they are combined), as well as the ability of the vaccine to adhere to and penetrate our cells will have an effect on how well the vaccine particles can be absorbed by the body. . this is called “bioviability” of the vaccine. We still need to know which application strategy is optimal for which vaccine.
Vaccines remain some of the best weapons we have against the pandemic.
This pandemic is still very much alive. And we’re learning more every day about the long-term implications of covid infections on our health, including heart complications and long-term covid.
This, coupled with the emergence of even more persistent variants, indicates how important it is to continue to protect ourselves and our loved ones from the worst effects of this disease. Vaccines are some of the best weapons we have.
It will be important to watch and learn from mucosal vaccination programs in other countries and check their data when they are launched.
In the meantime, given the urgency of long-term vaccines, it would be prudent invest in new strategies, not only for the development but also for the production of this type of vaccine. They would be a valuable tool against this pandemic and many other infections, including those we have not yet encountered.
*Sheena Cruickshank is Professor of Biomedical Sciences at the University of Manchester, UK. You can read her article in Englishhere
