As the pandemic continues, many countries are rolling out booster shots against COVID. In the UK, the fall booster campaign is offering a fourth dose to people at higher risk for COVID infection, including people with certain underlying medical conditions and people age 50 and older.
Fall booster shots are bivalent vaccinesmeaning they target the parent strain of SARS-CoV-2 (the virus that causes COVID-19) along with the omicron variant.
These vaccines are effective in complementing and amplifying our immunity. But we hope that, as we’ve seen with the original COVID vaccines, the protection they provide, particularly against infection, falls off in subsequent months.
Therefore, we must consider a vaccine strategy that provides longer-term immunity. A new kid on the block – mucosal vaccines – could offer promise on this front.
Mucosal vaccines are administered into the nose or throat, as formulations that are inhaled or inhaled. They may sound new, but we’ve actually been using them for years to vaccinate against illnesses like the flu.
While conventional needle-in-the-arm vaccines induce a more systemic immune response, mucosal vaccines do something different. Viruses like SARS-CoV-2 enter our systems through the nose and mouth when we breathe in small droplets that contain viruses. This means that immunity in our nose, mouth, and throat is really important in stopping infections.
Mucosal vaccines are designed to attack this.”mucosal immune system”. The mucosal immune system has the potential to stop the virus as it enters the body, so scientists predict that mucosal vaccines could prevent infection.
Mucosal immunity may also be better for our immune system to remember SARS-CoV-2. Memory cells are long-lived, specialized immune cells that remember the virus and carry instructions for our immune cells to rapidly deploy if it strikes again. Systemic vaccines are not as good at activating the memory cells in our nose and throat, but Mucous vaccines are.
Meanwhile, the fact that mucosal vaccines work locally could mean a a smaller dose is needed. This, coupled with less stringent storage requirements compared to some conventional vaccines, may mean that mucosal vaccines could be more efficiently deployed in resource-poor countries and be an important tool for vaccine equity.
Mucous vaccines would probably also be much more appealing to people with a phobia of needles. Barely 26% of the UK population admits to being afraid of needles, with the highest rates of the phobia seen in groups of young people, blacks, and Asians, groups that we know have lower consumption of vaccines and more doubts about vaccines.
The advantages are clear, but what does the evidence say?
Several mucosal vaccine candidates are being explored in preclinical and clinical trials. Newly published results on a nasal booster vaccine in mice showed that robust mucosal immune responses were induced in the nasal and upper airways.
Iran, Russia, India and China have already introduced mucosal vaccines despite published data on their vaccine candidates. remaining scarce. But some data has been made public.
The results of phase II human trials of an inhalable vaccine, now being implemented in Porcelainwere released as a preprint (a study that has not yet been peer-reviewed). While the study did not assess mucosal responses, it did show that systemic antibody levels were higher and remained higher over the six months tested compared to a conventional boost.
But the picture is mixed. A phase I trial of a nasal formulation of the Oxford AstraZeneca vaccine showed little or no induction of mucosal immunity and weaker systemic antibody responses compared to a conventional vaccine.
The reasons for these disparities are unclear, but could include the method of delivery. The administration of mucosal vaccines requires precise engineering and aerosol science to ensure that the small droplets containing the vaccine are easily inhaled.
Various strategies have been used to deliver mucosal vaccines, including nebulizers (a machine that turns liquids into a fine mist that can be inhaled), nasal sprays, and inhalable devices such as the 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 stick to and enter our cells will affect how well the vaccine particles are absorbed into the body. This is called the “bioavailability” of the vaccine. We still have a lot to learn about which delivery strategy is optimal for which vaccine.
Where does this lead us?
This pandemic is still ongoing. And we’re learning more all the time about the long-term implications of COVID infections on our health, including heart complications and long COVID.
This, added to the emergence of increasingly persistent variants, means that it is important to continue to protect ourselves and our loved ones from the worst effects of the disease. Vaccines are some of the best weapons we have.
It will be important to watch and learn from the launch of the mucosal vaccine in other countries and to analyze its data when it is published.
In the meantime, given the urgent long-term need for vaccines, it would seem prudent to invest in strategies, not only for the development but also for the manufacture of such vaccines. They could be an invaluable tool in this pandemic, but also against many other infections, including ones we haven’t yet faced.