“This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials,” AstraZeneca said in an emailed statement.
Below are reactions from scientists, drugmakers and stock market traders and analysts to the news:
Ian Jones, Professor of Virology at the University of Reading:
“An inevitable consequence of testing a vaccine on large numbers of people is that some will naturally fall ill of other causes during the trial.
We must wait and see what the investigation in this case shows but at the moment, I think unfortunate more than sinister would be the best description of the halt.”
Charlie Weller, Head of Vaccines Programme at Wellcome:
“Safety is the most important consideration when developing any vaccine, and it is right for the trial to be paused while an investigation takes place.
This is often a normal part of the process in vaccine trials, which involve tens of thousands of people. It’s critical to quickly understand whether the illness has any relationship to the vaccine or the placebo and to share data openly, as Oxford University and AstraZeneca have done.
“Vaccines are among the most rigorously tested and monitored products we have in society, and the Covid-19 vaccines should be no different.”
James Gill, Honorary Clinical Lecturer, Warwick Medical School, and Locum GP, said:
“During the development of any drug, people will develop side effects – hence we know ibuprofen can cause heart burn.
People will also fall ill during the natural course of their lives whilst they have taken the vaccine. We know that the flu vaccine doesn’t cause flu, but some people can be unlucky and catch a bug around the time they are inoculated.
Personally, I would be suspicious of a vaccine for a novel virus which was developed without any hiccoughs or pauses.
Science on TV is great, and usually gets completed in the course of an episode. In a real lab, chemistry, patients and biology don’t often follow a nice simple course, which is why from the start scientists have said that this Covid vaccine development will take considerable time to get right and safe.”
Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine:
“We do not know what event has occurred, but given that in the UK those aged over 70 have been included in the trials, coincidental events are to be expected.
Very occasionally, what might be expected in an older person, such as a stroke (and this is certainly not a suggestion that it is such an event that has happened here), can occur in a young person.
“This very incident shows that the Oxford trial, and any other trials conducted in the UK, are monitored very carefully and precautions are taken to protect both the trial participants and those who might get the vaccine in the future.
It is premature to speculate on whether the vaccine caused the adverse event, and even if it eventually is concluded that it is possible the vaccine was the cause, there may be other factors involved and it would not necessarily mean the vaccine could not be used at all.”
Germany’s Leukocare is working with Italy’s ReiThera and Belgium’s Univercells on a monkey adenovirus-based vaccine that is in early testing on humans.
CEO Michael Scholl said a clinical trial halt was not unusual:
“When you are inoculating 20,000 people, it is a foregone conclusion that at some point you will have severe adverse events. As soon as a link to the vaccine can clearly be ruled out, the trial continues.”
He added that something as common as a heart attack could halt a vaccine trial, though he cautioned that any immune-related condition such as an inflammation would be subject to particular scrutiny.
Moderna said it was “not aware of any impact” to its ongoing Covid-19 vaccine study at this time.
Serum Institute of India (SII):
“We can’t comment much on the UK trials, but they have been paused for further review and they hope to restart soon. As far as Indian trials are concerned, it is continuing and we have faced no issues at all.”
Traders and analysts:
AstraZeneca’s shares in London fell more than 3% at the open on the news. The FTSE-100 listed stock was down 1.5% at 0943 GMT.
Mirabaud trader Mark Taylor:
“These headlines will be set back, but it is not an unusual step in the process. The only unusual bit is the amount of attention being drawn to it.
“This dents the vaccine hope trade, which had become elevated and has been a major driver in some of the factor style rotation seen lately.”
Neil Wilson at Markets.com:
“Such are the problems with pinning hopes on a vaccine for a return to normal to be possible. The worry is that while we have all kind of assumed that one company will come up with a vaccine later this year, it’s not going to be plain sailing.”
“The risk of material potentially vaccine-related serious adverse event in one of the multiple large Covid-19 trials was always a high probability event.”
“(The) development may negatively impact timelines for other Covid-19 vaccine sponsors. While AstraZeneca’s current share price is discounting little economic value from Covid-19, we expect an initial negative stock and broader market reaction today in response to the news.”
“Even if the vaccine was to work, tolerability may be its Achilles heel and bigger picture, longer term safety of all vaccine candidates will remain an open question even if we get efficacy data later this year/early next.
For those that think the Oxford/AZN collaboration is a stepping stone into becoming a vaccine player, we remind investors AZN has repeatedly said that its involvement in the development of a SARS-Cov2 vaccine is not a commercial venture.”