US Trials For AstraZeneca COVID-19 Vaccine On Hold Amid Probe Into "Serious Side Effect"

Following AstraZeneca's weekend announcement that it had received the go-ahead to restart Phase 3 testing for its COVID-19 vaccine being developed in partnership with Oxford, Reuters has just reported that the trial remains on hold in the US pending an investigation into a serious side effect in the UK trials - even as other trials elsewhere have already resumed.

It's the latest blow to confidence in the company' s vaccine effort, which until now had until recently been considered one of the world's most promising partnerships, being among an elite group that was the first to make it to Phase 3 trials.

In its report, Reuters said a "serious side-effect" had piqued regulators interest. AZ caused a stir last week when it revealed that its trials had been put on hold after one patient came down with symptoms of a rare spinal inflammatory disorder called transverse myelitis, but on Saturday the company announced that trials would continue.

Here's more from Reuters:

CHICAGO, Sept 14 (Reuters) - AstraZeneca's AZN.L COVID-19 vaccine trial remains on hold in the United States pending a U.S. investigation into a serious side effect in Britain even as other trials of the vaccine resume, sources familiar with the details told Reuters.

AstraZeneca on Saturday said it had restarted its trial in Britain after regulators completed their review of a serious side effect in one trial participant there.

This was the first indication that the U.S. trial will remain on hold until the U.S. Food and Drug Administration and a safety panel investigate the case.

Enrollment in the company's global trials of the vaccine, which it is developing with researchers at Oxford University, was put on pause on Sept. 6.

Sources told Reuters that enrollment of new patients and other trial procedures for the pivotal U.S. trial were being rescheduled until at least midweek and that it was not clear how long it would take for the FDA to complete its probe.

Governments around the world are desperate for a vaccine to help end the pandemic, which has caused more than 900,000 deaths and global economic turmoil. The World Health Organization (WHO) had flagged AstraZeneca's as the most promising. A prolonged delay in the U.S. trial could slow access to the vaccine in the United States.

The British adverse event involved a study patient thought to be suffering a rare spinal inflammatory disorder called transverse myelitis.

The reaction in the market was surprisingly muted, considering that the "prolonged delay" - as Reuters put it - "could slow access to the vaccine in the United States."

An AZ spokeswoman declined to comment on the news, but said it "will continue to work with health authorities across the world, including the FDA, and be guided as to when other clinical trials can resume." Trials in Brazil, South Africa and India appear to be continuing on, which means they may still produce experimental data that the FDA could use toward an eventual emergency approval. But at this point, with the coronavirus global death toll now topping 900,000, the urgency is intensifying, and any delays for the top candidates are deeply problematic.