A recent clinical trial has found less-than-promising results for a nasally administered version of AstraZeneca’s COVID-19 vaccine, with immune responses only observed in “a minority of participants.”

University of Oxford researchers found in their Phase 1 clinical trial that not only were antibody responses only seen in a minority of participants, but these responses were also weaker in comparison to intramuscular vaccinations. The nasal formula that was administered was the same one used for intramuscular injections.

A nasal vaccine dose was administered to 30 participants who had not yet been immunized against SARS-CoV-2. Among those study participants, 14 received second nasal doses 28 days after their first dose.

Another 12 participants in the AstraZeneca-funded trial received mRNA coronavirus vaccines not made by the British-Swedish pharmaceutical company, whose own vaccine induces an immune response through a different system.

Following immunization, those who received intranasal vaccinations developed antibodies that “rarely” rose higher than the level of antibodies observed following a COVID-19 infection.

Researchers concluded that while the nasal vaccine was well tolerated, it “induced neither a consistent mucosal antibody response nor a strong systemic response.”

“The nasal spray did not perform as well in this study as we had hoped. This was quite different from recent data from China, which has suggested good results can be achieved by delivery of a similar vaccine deep into the lungs with a more complex nebuliser device,” said Sandy Douglas, an associate professor at Oxford University and chief investigator for the trial.

The Chinese vaccine that Douglas referred to was one made by the Chinese company CanSino Biologics. It was approved in September.

There are currently around 100 other similar mucosal vaccines being developed around the world. As noted in the peer-reviewed Nature science journal, one possible benefit of such vaccines is that they induce responses in the immune cells of the nose and respiratory tract, potentially acting much more quickly against infection.

Other human trials looking into the efficacy of intranasal vaccines are being conducted in countries like India, Mexico and the U.S.

Nasal vaccines are not an entirely new concept. A nasal vaccine is approved for use in the 2022-2023 flu season for healthy, non-pregnant people aged 2 to 49.

“We believe that delivery of vaccines to the nose and lungs remains a promising approach, but this study suggests there are likely to be challenges in making nasal sprays a reliable option,” Douglas said. “We urgently need more research to develop vaccines which can block transmission of respiratory pandemic viruses using delivery routes which are safe and practical at large scale.”