Confidential sources subsequently told various media organs said that the participant affected was enrolled in a company trial in the UK and had received a diagnosis of transverse myelitis, an inflammatory syndrome that affects the spinal cord and can be sparked by viral infections.

CEO Pascal Soriot later confirmed the information in a private briefing for investors, which was also leaked to the press. Soriot said the volunteer, a British woman, was expected to be released from hospital shortly. Transverse myelitis reportedly has also been observed in other vaccines, including those against hepatitis B, measles-mumps-rubella and diphtheria-tetanus-pertussis.

Halting a trial is a routine action that is mandated following any potentially unexplained illness and ensures that the integrity of the trial is maintained, the drugmaker said. In the next step, an independent panel will review the evidence and seek to determine whether the reaction was directly caused by the vaccine or coincidental.

AstraZeneca is currently conducting trials with the Covid-19ncandidate in England, India, Brazil, South Africa and the United States, with US enrollment targeted to reach 30,000 participants to meet the US Food and Drug Administration’s (FDA) threshold for considering a vaccine for approval.

In a paper published in British medical journal The Lancet in July, AstraZeneca’s researchers reported that the majority of participants in the vaccine’s Phase 1/2 trials had experienced only mild or moderate side effects, including muscle aches and chills.

The partnership of Oxford and AstraZeneca has received more than $1 billion in funding from the US Biomedical Advanced Research and Development Authority (BARDA). The drugmaker, which has already begun production, facilitated by its sponsors, has agreed to supply more than 300 million doses to the US government and has also pledged millions of doses to other countries.

AstraZeneca had expected to have its vaccine candidate ready for approval by the end of 2020. After pausing the trial, the company said in a statement that it is working to “expedite the review of the single event to minimize any potential impact on the trial timeline.”

If the reaction being investigated is found to be vaccine-related, the timeline could be endangered and public wariness potentially see a further increase. In the latest poll by US broadcaster CBS, only 21% of respondents said they would seek to receive a Covid vaccine as soon as one was available. This compares with 32% in July.

Pharmaceutical analysts commenting on the trial’s interruption were divided on what implications it might have for other vaccine candidates. In addition to the UK-Swedish drugmaker, CanSino Biologics and Johnson & Johnson are working on an adenovirus vaccine. The BionNTech/Pfizer partnership and Moderna are developing mRNA vaccines, while others are developing adjuvanted protein and inactivated vaccine candidates.

Author: Dede Williams, Freelance Journalist