AstraZeneca’s COVID-19 shot trials on hold after suspected reaction

Oxford and AstraZeneca’s COVID-19 vaccine trials put on a hold after a UK participant had a ‘serious’ suspected reaction to the leading shot candidate

  • Late stage trials for the vaccine being developed by AstraZeneca and Oxford University have been put on hold 
  • A ‘serious adverse event,’ a possible reaction to the shot was reported in the UK 
  • It’s not clear what happened to the individual, but an adverse event is considered ‘serious’ if it requires hospitalization, is life-threatening or deadly 
  • Stat News reported that the individual is expected to recover, but little else is known about their identity 
  • It is not clear if regulators, AstraZeneca or Oxford called for the trial hold
  • The shot was dubbed the best hope for a vaccine by the WHO and is one of nine in phase three trials – the last tests before approval can be sought  

Phase 3 trials for the coronavirus vaccine being developed by Oxford University and AstraZeneca have been placed on a hold after a ‘serious adverse event’ was reported in a participant in the UK. 

Serious adverse events are suspected reactions to vaccines or drugs that require hospitalization, are life-threateningly or deadly. 

It’s unclear what the exact nature of the reaction was, but a person familiar with the matter told Stat News that the person is expected to recover. 

Trial holds are not uncommon, but it is a blow to worldwide hopes for a shot to be ready in the coming months, as the AstraZeneca shot was considered by many – including the World Health Organization – to be the leading candidate worldwide. 

Development of the AstraZeneca vaccine and eight others in phase 3 trials is being closely watched in the hopes they can stem the coronavirus pandemic that has killed more than 894,000 people worldwide, including nearly 190,000 Americans, and cost tens of millions their jobs. 

It comes after vaccine developers – including AstraZeneca – pledged not to cut corners on safety and efficacy testing, despite US President Trump’s urgent push for the Food and Drug Administration (FDA) to give emergency approval to a vaccine ahead of the November 3 election.  

Phase 3 trials for the coronavirus vaccine being developed by Oxford University and AstraZeneca have been placed on a hold after a ‘serious adverse event’ was reported in a participant in the UK

‘As part of the ongoing randomised, controlled global trials of the Oxford coronavirus vaccine, our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee,’ an AstraZeneca spokesperson told

‘This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials. 

‘In large trials, illnesses will happen by chance but must be independently reviewed to check this carefully. We are working to expedite the review of the single event to minimise any potential impact on the trial timeline. We are committed to the safety of our participants and the highest standards of conduct in our trials.’  

AstraZeneca’s candidate vaccine, known as AZD1222, is in phase 3 trials – the final stage before safety and efficacy data can be submitted to regulators for approval – at dozens of sites across the US, and around the world. 

Trials for AstraZeneca's shot are underway in the US, UK, Australia, Brazil (pictured) and other nations. Phase 3 testing will now be paused while safety data is reviewed

Trials for AstraZeneca’s shot are underway in the US, UK, Australia, Brazil (pictured) and other nations. Phase 3 testing will now be paused while safety data is reviewed 

Along with Pfizer, and Moderna, AstraZeneca and its partner Oxford University had hoped to know whether the shot worked and was safe by year-end,. 

While trial holds to review safety data are not necessarily damning, the pause on AstraZeneca’s trial may very well delay the highly-anticipated results and completion of one of the fastest vaccine development pipelines in human history. 

Market confidence in the pharmaceutical giant took a hit as soon as reports of the trial hold emerged. 

Shares for AstraZeneca plummeted by eight percent in after-hours trading. 

President Donald Trump has hinted that he thinks a vaccine could be ready before a 'special date' - likely the November 3 election

President Donald Trump has hinted that he thinks a vaccine could be ready before a ‘special date’ – likely the November 3 election

The company is in now in mitigation mode to try to stay as close to its trial completion date as possible.

AstraZeneca is ‘working to expedite the review of the single event to minimize any potential impact on the trial timeline,’ the spokesperson told Stat News.   

Disconcerting though any signs that could suggest potential flaws in a leading vaccine for the disease that’s killed nearly 190,000 Americans is, the move to pause a trial over safety concerns may be reassuring to some. 

Hours before the trial was temporarily halted, AstraZeneca and eight other companies working on COVID-19 vaccines signed a pledge to prioritize safety of their shots over speedy development.  

They promised to ‘uphold the integrity of the scientific process as they work towards potential global regulatory filings and approvals of the first COVID-19 vaccine.’ 

The pledge was made in response to growing concerns that governments would press firms and research institutions to rush a vaccine through trials and approval processes in an effort to bolster political capital and restore normalcy amid the pandemic.  

Last week, the US Centers for Disease Control and Prevention (CDC) sent instructions to state health departments to prepare for the potential arrival of one of two coronavirus vaccines by the end of October. 

Subsequently, President Trump hinted at the hopeful possibility that a vaccine could be ready before a ‘special date,’ prompting speculation that he was referring to the November 3 presidential election – just days after the end-of-October potential finish line in the CDC guidance. 

Health officials like infectious disease expert Dr Anthony Fauci, US Surgeon General Dr Jerome Adams and Trump’s own vaccine czar Dr Moncef Slaoui were all quick to assure the American public that it was possible, but unlikely, that a shot would be ready by then, and that the FDA would pay no mind to the date, but only the data, to determine when a vaccine is ready for distribution. 

Pfizer, however, confirmed that it hoped to have sufficient trial data to know whether its shot was safe and effective by late October, and would submit for FDA approval ‘immediately’ afterwards. 

Most experts and observers speculate that the two unnamed shots referenced in the CDC guidance were Moderna’s and Pfizer’s, not AstraZeneca. 

The trial hold casts even further doubt over the possibility that the firm’s vaccine will be the first ready for the US market. 

Operation Warp Speed, the Trump administration’s effort to speed vaccine development, primarily by contributing funding to private companies working on shots, announced that AstraZeneca would be awarded up to $1.2 billion in funding for its vaccine development in May. 

The US has inked a deal with AstraZeneca for 300 million doses of its shot – if the vaccine is greenlit as safe and effective by the FDA – and had set its sights on an approval date as early as October, which seems increasingly improbable.