Vaccine 'accessory' found to stop Covid infection in the nasal tract

A nasal vaccine adjuvant, or a substance added to nasal vaccines to trigger a stronger immune response, was found to stop Covid-19 infection in both young and old mice.

Several current vaccines contain adjuvants, which boost the effectiveness of a vaccine.

While vaccines are known to offer protection against serious illness and death, vaccines can be improved in their ability to stop the spread of SARS-CoV-2 at the point of entry in the upper respiratory tract, the research led by the University of Michigan (U-M) and the Icahn School of Medicine at Mount Sinai, US, said.

Their vaccine protocol combines a nanoemulsion, similar to a tiny droplet of oil and water, and an RNA-based molecule, which is the adjuvant, recognised by the immune system.

The RNA adjuvant triggers antiviral pathways inside the cell while the nanoemulsion carries it into the cell, the study published in the journal NPJ Vaccines said.

This helps prevent the adjuvant from being cleared too quickly from inside the nasal passages, along with activating immune pathways complementary to the one triggered by the RNA adjuvant, it said.

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Testing the combined vaccine, including the adjuvant, the researchers detected an enhanced antibody and memory T cell response in both young and old mice, including in the mucus-secreting membrane lining of the upper airway where the virus starts to proliferate.

"It's very hard to induce a strong immune response with intranasal vaccines containing just the protein or inactivated virus alone because your mucosal sites will see many things during the day or over a lifetime and are to some extent 'trained' not to overreact.

"So, you want to overcome that barrier through the use of adjuvants while balancing safety," said Michael Schotsaert, co-corresponding author of the study and an assistant professor of microbiology at Icahn Mount Sinai.

Further, the nanoemulsion can inactivate viruses on its own, the researchers said.

"This means you could mix live virus with the nanoemulsion and it would inactivate it without having to use harsher chemical methods, better preserving the conformation of the viral proteins that the immune system sees, potentially leading to better quality immune responses," said Pamela Wong, a research assistant professor in the U-M Medical School.

The team plans to pursue further studies for bringing the adjuvant to Phase 1 safety trials, along with exploring its applications for a universal flu vaccine.

"There is considerable interest in intranasal vaccines for respiratory viruses because inducing mucosal immunity can help prevent viral transmission, whereas injectable vaccines don't effectively elicit mucosal immune responses," said Wong.