A nasal version of the Oxford/AstraZeneca Covid-19 vaccine has failed in an early-stage trial, dealing a blow to hopes for a more effective way to prevent transmission of the virus.

Oxford university said on Tuesday a nasal formulation of the vaccine elicited mucosal antibody responses in a “minority of participants” and systemic immune responses were also weaker compared with intramuscular vaccination.

The setback highlights the complexity of designing a nasal formulation against coronavirus, which spreads through tiny particles in the air. Researchers have posited that targeting the airways could effectively prevent transmission of the disease. Currently available vaccines, delivered as intramuscular injections, only offer limited protection against contagion, although they retain significant effectiveness against more severe outcomes.