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The candidate from the University of Oxford and Astrazeneca temporarily interrupts phase 3 when a vaccinated person falls ill. Aragonese researchers analyze the situation.
The large phase 3 trial, with thousands of volunteers of one of the most advanced Covid-19 vaccine candidates in the world, the one developed by the University of Oxford and the pharmaceutical company Astrazeneca, has been temporarily interrupted after one of the volunteers fell ill. volunteers. It is time to stop vaccination until we know whether the adverse effect detected is due to the vaccine or not.
"This interruption of vaccination indicates that we can trust that the vaccine has passed the most demanding safety filters"
"The news sounds very sensational, that's what it means to narrate a clinical trial in real time," says Ignacio Aguiló, coordinator of the immunity team of the group at the University of Zaragoza that develops the new vaccine against tuberculosis, MTBVAC. Actually, "what has happened with the Oxford vaccine is not strange to happen and what it indicates in principle is that the vaccine development process works, which is a guarantee that the vaccine will be safe once it is licensed; indicates that we can trust that it has passed the most demanding security filters".
"There is currently no vaccine based on viral vectors in use, so it is understandable that safety studies are being carried out to the extreme"
Carlos Martín, head of this Mycobacterial Genetics Group, specifies that "the Oxford vaccine is based on a DNA virus vector (which encodes the S protein of SARS-Cov-2, which binds to cells). and there is currently no vaccine based on viral vectors in routine use, so it is understandable that safety studies of this new vaccine are being carried out to the extreme."
Thousands of volunteers
Phases 1, 2 and 3 of clinical trials "are progressively scaled, going from dozens to hundreds and then thousands of volunteers, respectively," recalls biochemist Jesús Gonzalo, a researcher in this same Unizar group. For this reason, "as clinical trials progress, the probabilities of detecting strange effects (such as the one that appeared in the Oxford vaccine trial) increase for a simple fact: the number of vaccinated is greater."
"As the phase of clinical trials advances, the probability of detecting strange effects increases because the number of vaccinated is greater."
Specifically, the Oxford and Astrazeneca trial "is analyzing in depth the health of 30.000 people. Statistically, it is not unusual that something like this could happen," says Aguiló.
During clinical trials with vaccines, "there is a whole legion of personnel monitoring the volunteers and classifying all adverse effects as mild, serious or very serious," says Aguiló. At the same time, "there is a committee of medical experts called DSMB (Data Safety Monitoring Board), which has to ensure the safety of the study and has the power to stop the trial at any time when something happens." DSMB experts are required to be independent to ensure objectivity.
In this case, since a serious adverse effect was found in one of the volunteers, the trial has been interrupted. "The normal thing is that the DSMB decides to stop the study to analyze the data and see if the effect is associated with the vaccination or not and if it has only occurred in that volunteer or also in others," says Aguiló. Does this mean that they are going to stop the study? "If it is a specific event as it seems to have been and they see that the vaccine is safe, it is most likely not. The logical thing is that in a few days the DSMB will give the OK again for the trial to continue," he says. "It is a matter of caution, and it is common in clinical trials."
Regarding the impact of this fact on the planned schedule, Aguiló indicates that "if the effect has occurred in only one volunteer, it should not take more than a few days until the trial continues. The realistic forecasts or not of a vaccine as a solution to the pandemic In the short term they will have more to do I suppose with whether the vaccine really works, in what percentage it works, in what populations it works or simply in what time scale the industry will be able to produce the global demand for vaccines.
