In a study from the University at Buffalo, scientists found that substantial immunity against the SARS-CoV-2 virus will only happen with a vaccine that can be delivered through the nose.
They suggest the best protection against initial infection with the coronavirus, as well as transmission of it, as opposed to the development of COVID-19 disease, will be most effectively achieved by intranasal vaccines.
The reason is that the most robust immunity against COVID-19 comes about as a result of the infection that takes place in the upper respiratory tract and the mouth, and gives rise to mucosal immunity through the secretion of Immunoglobulin A (IgA) antibodies.
Evidence is accumulating that shows that mucosal IgA antibodies have a significant impact on the acquisition of SARS-CoV-2, the subsequent course of the disease, and further transmission of the virus.
Vaccines delivered through the nose would not only induce mucosal immunity and thus prevent individuals from becoming infected, but they could also suppress community spread, which results from the circulation of aerosol particles and droplets generated by these upper respiratory and oral secretions.
The team suggests that protection against initial infection (rather than protection against the development of COVID-19) and the onward transmission of the virus will be more effectively achieved by intranasal vaccines.
In other words, the much-discussed and elusive accomplishment of herd immunity, which is not effectively generated by the existing injected vaccines, will be more likely to be achieved with mucosal immunity induced by intranasal vaccines.
The paper also argues that despite the fact that antibody responses to COVID-19 have almost entirely focused on serum, it turns out the level of antibodies that are circulating in the blood doesn’t reflect the antibody level in mucosal secretions.
Meanwhile, mucosal IgA antibodies to SARS-CoV-2 antigens have been detected in the saliva, nasal fluids, tears, tracheo-bronchial secretions, and even breast milk in infected people.
The team conceded that while there have been numerous animal model trials launched to develop intranasal vaccines against SARS-CoV-2, many haven’t continued past the preclinical stage.
In part, this might be due to an inadequate understanding of how the human and animal mucosal immune systems differ.
The authors noted that the success of the influenza vaccines delivered through the nose indicates that this is a feasible delivery method for a vaccine.
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The study was conducted by Michael Russell et al and published in Frontiers in Immunology.
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