AstraZeneca Shares Drop 8% As Advanced COVID-19 Vaccine Trials Are Halted

AstraZeneca Plc AZN shares tanked in the after-hours session Tuesday, as the British drugmaker said it has temporarily halted the advanced trials of its COVID-19 vaccine to allow for a review of safety data by an independent committee.

What Happened: The company said the stopping of the trial was a routine action after any participant develops an unexplained illness, according to Reuters.The British drugmaker reportedly said it is working so that the review can be carried out expeditiously without impacting the trial’s timeline.

The Phase 3 study of the vaccine was suspended after a serious adverse reaction in a participant in the United Kingdom, according to a Stat report.

A person familiar with the matter told the publication that the suspension would have an impact on other AstraZeneca trials underway as well as affect vaccine trials being conducted by various manufacturers.

Why It Matters: The Cambridge, United Kingdom-based company began the Phase 3 trials for its COVID-19 vaccine, jointly developed with the University of Oxford, in late August in the United States at 62 sites, although some of these sites have not yet enrolled participants. Trials are also underway in U.K., Brazil, and South Africa. 

Brazil’s health regulator Anvisa said Tuesday that the company has informed it of trial suspension, including the one underway in the country, Reuters reported separately. 

Chief executives of companies that are leading the trials pledged Tuesday not to expedite the COVID-19 vaccine at the cost of safety. The signatories include CEOs of AstraZeneca, BioNTech SE BNTX, Pfizer Inc PFE, Moderna Inc MRNA, Johnson & Johnson JNJ, and GlaxoSmithKline Plc GSK.

The Centers for Disease Control and Prevention had notified all 50 states last week to begin preparations for distributing two unnamed vaccines thought to be those from Pfizer and Moderna.

The guidelines from the agency came the same day President Donald Trump said a vaccine could be ready before the end of the year.

Price Action: AstraZeneca shares closed nearly 2.1% higher at 54.71 on Tuesday and declined almost 8.1% in the after-hours session to $50.30.