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Nasal Spray Reduces Flu Duration in Challenge Trial

3-D print of influenza virus

3-D print of influenza virus (National Institute of Allergy and Infectious Diseases, NIH)

13 Feb. 2023. An influenza vaccine given as a nasal spray is shown in a clinical trial to reduce the amount of time participants have flu infections, when exposed to the virus. Results of the trial are reported today by ENA Respiratory Pty. Ltd., developer of the vaccine on the company’s web site, and are not yet peer-reviewed.

ENA Respiratory is a three year-old enterprise in Melbourne, Australia, creating antiviral treatments for respiratory diseases, including Covid-19 and influenza. While Covid-19 captured much of the world’s attention since it emerged in Dec. 2019, influenza remains a serious global threat to public health. According to World Health Organization, some 3 to 5 million seasonal flu cases occur every year, resulting in up to 650,000 deaths. Influenza is a particular risk for complications and severe symptoms in children under five years of age, pregnant women, and older people.

The company’s lead product, code-named INNA-051, is designed as a self-administered nasal spray, given once or twice a week, to prevent viral infections. INNA-051, says ENA Respiratory, are stimulators of toll-like receptors or TLRs, proteins in the immune system that in this case promote an innate immune response in the nasal mucous membranes. The company says its preclinical studies show INNA-051 can help prevent a number of respiratory viral infections including influenza, SARS-CoV-2 responsible for Covid-19, and rhinovirus associated with common-cold symptoms. An early-stage clinical trial reported by ENA Respiratory at an American Thoracic Society meeting in May 2022, shows INNA-051 is well-tolerated among healthy volunteers with no more than mild localized reactions in the nose, and no systemic adverse effects reported.

More participants with immunity than expected

The latest clinical trial is a mid-stage study enrolling 123 healthy adults, age 19 to 53, in the U.K. Participants were randomly assigned to receive either a high or low dose of INNA-051, or a placebo nasal spray, at four and two days before being purposefully infected with an H3N2 influenza A virus. The study team then took polymerase chain reaction or PCR tests of viral load during the eight days after the viral challenge, and also assessed participants for signs of adverse effects.

ENA Respiratory reports the trial did not quite proceed as planned. The company expected most of participants to become infected, but found a large percentage of those enrolled had a pre-existing immunity to the flu strain used in the challenge. As a result, fewer than anticipated numbers became infected, particularly in the placebo group. Nonetheless, says ENA Respiratory, participants becoming infected and receiving INNA-051 have shorter amounts of infection time than placebo recipients, with differences large enough for statistical reliability. And, says the company, safety findings mirrored those in the early-stage trial, with at most mild and short-lived localized reactions.

“In this study,” says  ENA Respiratory CEO and managing director Christophe Demaison in a company statement, “INNA-051 was found to be safe and to significantly impact the course of infection. We are eager to investigate INNA-051’s clinical benefit in the context of natural viral respiratory tract infections in individuals at increased risk of more severe illness.”

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