AstraZeneca Plc’s ambitions for developing an easier formulation of its COVID-19 vaccine -- one that might help curb contagion as well -- suffered a setback Monday as the nasal spray failed in an early test.

The spray vaccine didn’t elicit a strong immune response in the nasal mucosa tissue or in the rest of the body of volunteers, according to researchers at the University of Oxford. Astra shares fell less than 1 percent in London.

The UK drugmaker was one in a handful of companies investigating the approach, arguing a nasal inoculation can thwart the virus at its point of entry. Others include Meissa Vaccines Inc. In India and China, Bharat Biotech International Ltd. and CanSino Biologics Inc. have nasal products that won clearance as boosters from local regulators.

The Astra trial’s lead investigator, Sandy Douglas, said the setback suggests “there are likely to be challenges in making nasal sprays a reliable option.

The vaccine was studied in 30 people as an initial immunization and in 12 as a booster. Peer-reviewed data backing the nasal products approved in China and India hasn’t been released, according to Douglas.

“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,” he said in a statement.

Andrew Freedman, a reader in infectious diseases at Cardiff University, called the trial results disappointing and also said they shouldn’t “deter further work” to develop more effective intranasal vaccines to protect against COVID-19 and other respiratory infections.

Astra’s injected COVID-19 vaccine, also developed with scientists at Oxford’s Jenner Institute, hasn’t been as widely used as messenger RNA shots from Moderna Inc. and the partnership of Pfizer Inc. and BioNTech SE.

Astra also makes Flumist, a flu vaccine in nasal spray form, which has been seen as an alternative to needles that can potentially give protection at the site of viral attack, the respiratory tract.

The Oxford trial, supported by Astra and the NIHR Oxford Biomedical Research Centre, began in mid-2021, ended in 2022 and didn’t exclude participants based on prior infections. Douglas said that possible causes of failure include that the vaccine might get swallowed and destroyed in the stomach. The findings were published in the The Lancet’s eBioMedicine open access journal, the statement said.