Safety is paramount in vaccine clinical trials and temporary suspensions are not unusual to evaluate any unexplained illness in a participant, the World Health Organisation (WHO) has said regarding the pause in an AstraZeneca Covid-19 trial.

AstraZeneca has suspended global trials of its experimental coronavirus vaccine after an unexplained illness in a participant, knocking the British drugmaker's shares on Wednesday as prospects for an early rollout dimmed.

“We are pleased to see vaccine developers assuring the scientific integrity of the trials and abiding by the standard guidelines and rules for the development of vaccines,” the WHO said by email in response to a Reuters query.

The WHO recommended “strict adherence to established testing protocols in all vaccine trials to ensure the safety of volunteers and the eventual safety and efficacy of vaccines”, it added.