The University of Oxford, in an official statement, said that the antibody response in the respiratory mucous membranes was seen in only a minority of participants in the trial, which was in the first of usually three phases of clinical testing.
Also, it also showed that the immune response measured in the blood was weaker than that from a shot-in-the-arm vaccination, the statement said as quoted by Reuters.
However, researchers across the world had high hopes for the nasal spray Covid-19 vaccine because the method is believed to potentially prevent infection and not just disease as it may prompt an immune response directly in the airways, where the virus enters the body.
Additionally, the method would also be less painful and easier to handle than injections.
Meanwhile, the regulators in India and China have already cleared products that are administered through the airways.
Last month, India's health minister approved Bharat Biotech's COVID-19 nasal spray vaccine while China's CanSino Biologics Inc won emergency approval by the country's drug regulator for an inhaled version of its COVID-19 vaccine.
CanSino has said studies indicated that its vaccine, delivered via a nebulizer device, can induce strong immunity to effectively contain an infection, while Bharat's trial results have not yet been published.
The British trial enrolled 30 previously unvaccinated participants as well as 12 volunteers, who had previously received a standard two-dose vaccine course by injection.
Sandy Douglas, chief investigator of the trial at Oxford University's Jenner Institute said, "The nasal spray did not perform as well in this study as we had hoped."
"We believe that delivery of vaccines to the nose and lungs remains a promising approach, but this study suggests there are likely to be challenged in making nasal sprays a reliable option," she added.
No serious adverse events or safety concerns were reported during the trial, which was funded by AstraZeneca, the statement added.
(With Reuters inputs)
