Late-stage human trials for a leading Covid-19 vaccine candidate have been paused after a participant fell ill, but experts contend it is still too soon to say if the vaccine caused the illness.
"This is how clinical trials work," said Professor Ooi Eng Eong, deputy director of Duke-NUS Medical School's emerging infectious diseases programme.
Before the start of every clinical trial, scientists and clinicians will first define a list of "serious adverse events", he explained.
"This could include hospitalisation or death from any cause - including a road traffic accident."
Once the trials commence, the occurrence of any of the events on the pre-defined list would be enough to cause a pause in the trial as the researchers undertake a full review of the situation, said Prof Ooi.
"In this case, we need to wait for more data before we can know if the vaccine had caused this outcome."
The Covid-19 vaccine, which pharmaceutical company AstraZeneca is developing with the University of Oxford, is considered one of the leading candidates. The drugmaker said in a statement that the voluntary pause is a routine action which has to happen whenever there is potentially unexplained illness in any trial as it is being investigated.
The firm did not give details about the case but The New York Times reported that it was a volunteer in the British trials, who was diagnosed with transverse myelitis, an inflammation of the spinal cord generally caused by infections.
The incident raised questions about whether the speed of the search for a Covid-19 vaccine had led to any compromise in safety procedures.
But this is not necessarily the case, said Prof Ooi, a co-developer of a Covid-19 vaccine currently undergoing early-stage human trials in Singapore.
"Accelerating vaccine development does not mean that safety measures are foregone," he said.
It is the advent of new technology, such as molecular tools, that allow scientists to evaluate the safety and efficacy of a vaccine even before it reaches the human trial stage.
"That makes it easier to move it along faster. But there are no shortcuts in the clinical trial process."
The Ministry of Health's director of medical services Kenneth Mak told a press conference yesterday the pause in the trial is a safety measure that is not uncommon in many trials.
"This can occur very easily with any other vaccine. And this is why we've always been sharing that the road towards vaccine development is long and can be difficult," said Associate Professor Mak.
"We continue to watch very closely the conduct of these studies to make sure the vaccine candidates that are currently promising really can deliver on their potential."
