An experimental single-dose, intranasal influenza vaccine was safe and produced a durable immune response, a Phase I study has shown. 

The investigational vaccine, called Ad4-H5-VTN, is a recombinant, replicating adenovirus vaccine designed to spur antibodies to haemagglutinin, a protein found on the surface of influenza viruses that attaches to human cells.

The investigational vaccine was developed by Emergent Biosolutions. It was administered intranasally in 28 study participants, as an oral capsule in 10 participants and via a tonsillar swab in 25 participants, to healthy men and non-pregnant women ages 18 to 49 years.

The participants who received the vaccine intranasally or via tonsillar swab showed significantly higher H5-specific neutralising antibody levels compared to the group receiving the vaccine capsule orally. The participants who received the intranasal vaccine shed viral DNA for two-to-four weeks, but virus could be cultured for a median of only one day. Participants had evidence of H5-specific CD4+ and CD8+ T-cell responses. Additionally, volunteers who received the intranasal vaccine had high levels of serum neutralising antibodies at 26 weeks after vaccination and this level was unchanged at three to five years after a single intranasal dose of the vaccine. The duration of viral shedding correlated with a high magnitude of neutralising antibody response at week 26. In addition, the intranasal vaccine induced a mucosal antibody response in the nose, mouth and rectum.

The study authors speculate that replication-competent vector vaccines may have advantages over other types of vaccines because they can express viral proteins at higher levels and for longer durations. Additionally, this type of vaccine induces a mucosal immune response that is critical for limiting transmission of viruses that infect mucosal tissues.

The vaccine platform could be highly adaptable for use against other viruses including HIV and SARS-CoV-2, according to the authors.

The study results were published in the Journal of Clinical Investigation.