Intranasal Flu Vaccine Shows Promise in Clinical Trials

One day, a flu shot (influenza vaccine) administered nasally might replace our current shot-in-the-arm technique. A phase one clinical trial on the effectiveness of an intranasal influenza vaccine has shown promise by activating a strong immune response in 28 study participants.

The results also confirm that a mucosal antibody reaction could provide long-lasting immunity to upper respiratory viruses including influenza, HIV, and SARS-CoV-2, the virus that causes COVID-19.

The investigational intranasal vaccine, created by Emergent Biosolutions Inc., is a recombinant, replicating adenovirus that was designed to develop antibodies to the protein found on the surface of the influenza virus.

Compared to the traditional flu vaccine—which is made using animal cells or grown in fertilized chicken eggs, then administered by intramuscular injection—the design of the intranasal vaccine allows it to produce a more durable immune response.

“Durability is one of the advantages of an intranasal adenovirus vaccine,” Mark Connors, MD, chief of the HIV-Specific Immunity Section at the National Institute of Allergy and Infectious Diseases Laboratory of Immunoregulation and co-author of the new research on the intranasal flu vaccine, tells Verywell. “It produces long-term mucosal immunity, and when tested in animal models, it shuts the virus down.”

Intranasal Vaccines Versus Traditional Flu Shots

Historically, vaccination has been an important tool for reducing the incidence of influenza illness and hospitalizations related to the infection. However, flu shot effectiveness varies.

A 2011 study found that the current flu vaccines—which include both inactive and live-attenuated (weakened) vaccines—are only 59% effective in adults ages 18 to 65.

These findings highlight why new vaccines need to be created to improve clinical efficacy and effectiveness. Vaccines need to be able to keep up with the widely mutated influenza strains that we are presented with each year.

Are Intranasal Vaccines More Effective?

The intranasal influenza vaccine uses a weakened adenovirus—for example, the common cold—as a vector to introduce the foreign antigens needed to produce a robust immune response. The traditional flu vaccine uses a killed or weakened version of the influenza virus to produce an immune response.

Since influenza is a contagious respiratory virus that infects the nose, throat, and sometimes the lungs, introducing a vaccine at the local level (intranasally) can produce a highly effective and stronger mucosal immune response. This, in turn, results in longer immunity and is critical for preventing the transmission of respiratory viruses that infect the mucosal tissue.

“Producing mucosal immunity locally is the first advantage of the intranasal influenza vaccine,” Connors says. “This route could also be promising in other respiratory infections including HIV and SARS-CoV-2.”

Why We Need New Vaccines

With the COVID-19 pandemic and the need to mass vaccinate a large population, intranasal vaccines may emerge as a cost-effective measure to not only improve existing influenza vaccine technology but as a strategy to prepare us for future pandemics.

The authors of a 2016 study on the current prospects and future challenges of nasal vaccine delivery noted that with the "increased need to immunize large populations, potentially in swift response to pandemics, there is a clear need to have strategies in place.”

The study also highlighted that while there is a great deal of research underway to advance the design of intranasal vaccines, these studies face several challenges—such as the high cost of clinical trials and the correlating immune responses in animal models with humans. 

The COVID-19 pandemic also accelerated the use of a breakthrough vaccine technique. In just 10 months, researchers were able to create safe and effective vaccines using synthetic mRNA—a technology that could change vaccines forever.