The Oxford/AstraZeneca Covid vaccine performed poorly in its first clinical trial, dealing a blow to hopes of distributing it as a spray.
The disappointing results have led scientists to abandon plans to develop the spray in its current form, with hopes now resting on different versions of the vaccine and more complex delivery devices.
Sandy Douglas, the chief investigator on the trial, said that the spray did not perform as well as they had hoped. The delivery of vaccines to the nose and lungs is a promising approach, but this study suggests there are likely to be challenges in making nasal sprays a reliable option.
The potential to slash transmission by blocking the virus at the point of entry into the body is one of the reasons why researchers have been interested in developing a vaccine for Covid. Existing vaccines are very good at preventing disease, but they aren't very good at controlling the spread of the virus.
The efficacy of the Oxford vaccine was tested in a phase 1 trial. 30 people who hadn't previously received a vaccine against Covid were part of the trial.
The spray produced weak and inconsistent immune responses which were insufficient to warrant further development of the current combination.
The scientists were able to measure the levels of both mucosal and systemic antibodies against Covid. There wasn't much evidence of an immune system after a single spray. After two doses, a few participants had mucosal antibodies, but they were not as high as those seen after Covid infections.
After one or two sprays of the spray, only a fraction of the trial volunteers had a measurable response to Covid, and levels were typically lower than those seen after two jabs of the same vaccine.
China and India recently approved two new Covid vaccines. China's Covid booster is administered through a nebuliser that turns the vaccine into a mist. India's vaccine uses drops in the nose to deliver a two-shot vaccine.
It is possible that the majority of the Oxford spray will end up in the stomach rather than in the nose, throat, and lungs. To get around this, the vaccine could be reformulated to make it stick to the respiratory tract.
Prof Gordon Dougan said that although the results were not promising, the data was very helpful for the field because of the difficult nature of the vaccine. He said that better science is needed to understand how to induce immunity. It's not understood.
It will be important to prevent the emergence of vaccine escape variant because of the chance to induce local immunity from nanals.
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