A new approach to a Covid-19 nasal vaccine shows early promise
A new approach to a Covid-19 nasal vaccine shows early promise
German researchers have developed a nasal vaccine that prevents the virus from replicating in the nose and throat, where it initially enters the body. In trials with hamsters, two doses of the vaccine—using a live but weakened form of the coronavirus—successfully halted viral replication in the upper airways, achieving “sterilizing immunity” and blocking illness. This outcome marks a significant milestone in the fight against the pandemic, as such immunity had long been a sought-after goal.
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While this vaccine faces additional challenges before reaching public health systems, other nasal vaccines are already in use or approaching clinical trials. China and India launched their own nasal-based vaccines last fall, though their efficacy in humans remains uncertain. Research on these vaccines’ effectiveness has not yet been published, leaving many to question their real-world impact.
The U.S. remains in a stalemate with the virus. Despite the pandemic’s darkest days passing, hundreds of Americans continue to die daily as the infection lingers in daily life. Ongoing transmission among people and animals keeps the threat of new, more dangerous variants alive. For most healthy individuals, the virus is now manageable, but it still poses risks to the elderly and immunocompromised.
“If they are already on site, they can immediately eliminate the fire, but if they’re like 2 miles away, they first need to drive there, and by that time, one-third of the house is already in full flames,” said Emanuel Wyler, a scientist at the Max Delbruck Center for Molecular Medicine in Berlin.
Researchers hope next-generation vaccines can offer stronger protection by targeting the upper airways directly. This strategy focuses on boosting mucosal immunity, which strengthens defenses in the tissues lining the respiratory tract—where the virus first encounters the body. Unlike traditional shots, which primarily stimulate immune responses in the bloodstream, mucosal vaccines may activate a faster, more localized reaction.
One key advantage of mucosal immunity is its ability to generate IgA antibodies, which have four binding sites to grasp invaders. In contrast, IgG antibodies, shaped like the letter Y, only have two arms. Some scientists suggest IgA might be more versatile in recognizing new viral variants, potentially offering better defense against mutations.
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The new nasal vaccine leverages a century-old technique: weakening a virus to make it harmless and then introducing it to train the immune system. Early vaccines against anthrax and rabies used heat or chemicals to reduce virulence, but modern methods rely on genetic engineering. By altering the virus’s genetic material, scientists prevent cells from translating its instructions effectively, halting replication without causing disease.
“You could imagine reading a text … and every letter is a different font, or every letter is a different size, then the text is much harder to read,” Wyler explained. “This is basically what we do in codon pair deoptimization.”
Published in the journal Nature Microbiology on April 3, 2023, the hamster study revealed that two doses of the live weakened vaccine triggered a stronger immune response than mRNA or adenovirus-based alternatives. The researchers believe the live vaccine’s effectiveness stems from its ability to closely mimic natural infection, allowing the body to build defenses more efficiently.
