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Nearly 100 Covid-19 vaccines are currently in clinical trials around the world, out of which only seven are delivered intranasally. Injection pain is one of the reasons for vaccine hesitancy among people. Intranasal Covid-19 vaccines are needle-free, means pain-free. In a new article published in the journal Science, two immunologists from the University of Alabama at Birmingham (UAB) have highlighted several advantages of using an intranasal vaccine against the SARS-CoV-2 virus in the fight against COVID-19 pandemic.
In the article, UAB researchers - Fran Lund and Troy Randall also pointed out individual advantages and challenges of each of the seven intranasal vaccine candidates under clinical trials. Lund is a professor of microbiology and Randall is a professor of medicine in the Division of Clinical Immunology and Rheumatology at UAB.
According to the UAB researchers, the main advantages of intranasal vaccines are needle-free administration, delivery of antigen to the site of infection, and the elicitation of mucosal immunity in the respiratory tract.
Compared to intramuscular shots, intranasal vaccination also gives two additional layers of protection. A vaccine administered through the nose produces: 1) immunoglobulin A and resident memory B and T cells in the respiratory mucosa that are an effective barrier to infection at those sites, and 2) cross-reactive resident memory B and T cells that can respond earlier than other immune cells if a viral variant does start an infection.
According to the UAB researchers, six of the seven intranasal vaccine candidates are viral vectors, including three different adenovirus vectors, and one candidate each for live-attenuated influenza virus, live-attenuated respiratory syncytial virus and live-attenuated SARS-CoV-2. Only one vaccine candidate is an inert protein subunit.
Talking about some of the challenges of these nasal vaccines, the UAB immunologists said that using viruses that people may have already encountered before is negative interference from anti-vector antibodies that may impair vaccine delivery. Citing the minimal risk of reversion for the live-attenuated SARS-CoV-2 virus, they said this approach may be contraindicated for infants, people over 49 and immunocompromised persons.
"Notably absent from the list of intranasal vaccines are those formulated as lipid-encapsulated mRNA," Lund and Randall said, as quoted by Science Daily.
The ultimate goal of vaccination is to elicit long-lived protective immunity, and therefore, effective vaccination need not be restricted to a single route, noted the UAB researchers.
Suggesting the ideal vaccination strategy, Lund and Randall said that we, "may use an intramuscular vaccine to elicit a long-lived systemic immunoglobulin G response and a broad repertoire of central memory B and T cells, followed by an intranasal booster that recruits memory B and T cells to the nasal passages and further guides their differentiation toward mucosal protection, including immunoglobulin A secretion and tissue-resident memory cells in the respiratory tract."
In India, Hyderabad-based Bharat Biotech is working on a nasal vaccine, called BBV154, which is under Phase I trials. The company, which also manufactures Covaxin, is expected to roll out 10 crore doses of its nasal vaccine by the end of the year.