WHEN A VACCINE TRIAL RUNS INTO A HURDLE AT PHASE 3
On Tuesday, British drug major Astrazeneca voluntarily suspended clinical trials in the UK for the vaccine candidate developed by the University of Oxford after an event of suspected adverse side effect came to notice. A lot is riding on what is dubbed as one of the front runners for Covid-19 vaccines. When are vaccine trials paused? And what happens now? Let’s find out.
Why was the Covishield trial paused in the UK?
The UK arm of the Covishield trial reported an incident of serious illness that needed hospitalisation, but the cause was unexplained. There is, thus, a possibility that the trial participant may have experienced the sickness due to an adverse reaction following the administration of the vaccine.
What is the general process of clinical trials of a vaccine candidate?
There are quite a few stages of clinical trials to investigate a vaccine candidate. First, it is tested on animals — both small and large. These are called pre-clinical trials. Investigators typically check for immunogenicity (immune response) and safety profile of a candidate. In case of the Oxford-astrazeneca candidate, trials were done on monkeys.
Human trials begin with Phase 1, which involves giving vaccines to volunteers with informed consent and then looking for adverse effects. There are two kinds of adverse effects: Any toxic effect on any human body tissues (picked up by symptoms or biochemical parameters in blood); or if one develops any adverse immune reactions.
In the Phase 1 of clinical trials, usually carried out on a small group of people (a few dozen), researchers check whether the vaccine candidate is safe or not, meaning whether or not it induces any harmful side effects in the human body.
The Phase 2 trials, usually carried out on a few hundred participants, are mostly about checking whether the vaccine triggers adequate immune response in the body.
The third phase, of several thousand participants, is the most comprehensive and also the most time-consuming. In Phase 3 trials, people with underlying conditions, weaknesses or diseases also participate. They have to be RTPCR negative for the Sarscov-2 infection. In Phase 3, some adverse reactions are not uncommon.
After each phase, the data is collated and put before the ethics committee that comprises experts from different fields. Once the committee is satisfied with the data, it gives a green signal to proceed to the next stage. Each clinical trial site has an ethics committee.
Have vaccine trials been dropped in late-stage clinical trials?
Most HIV vaccine trials have not been successful. GSK’S MAGE-A3 vaccine candidate was dropped due to lack of efficacy. Late-stage trials of Takeda Pharmaceutical’s dengue vaccine failed to protect against one of the four types of the virus. Sanofi’s dengue vaccine Dengvaxia, which was approved in late 2015 as the world’s first vaccine to treat the condition, ran into controversy after it was introduced in the Philippines. It actually increased the risk of severe dengue in people who had not been exposed to the disease previously.
When can the Covishield trials re-start?
The restart of the vaccine trials will depend on the UK medical regulator, the Medicines and Healthcare Products Regulatory Agency. Once it reviews the situation, analyses the cause of unexplained illness in the participant, and is convinced that the vaccine is safe for administering, the trials can re-start. International media reports claim that it can be a matter of a few days or weeks.