On late Monday night, the pharmaceutical company Johnson & Johnson put a temporary pause on all of its clinical trials of experimental vaccines for the coronavirus that causes covid-19, following the report of an “unexplained illness” in one of the study participants. It’s not yet clear whether the person’s illness is connected to the vaccine, nor the exact nature of their ailment.
The pause was first reported by STAT News, an hour before the company announced the decision. According to J&J, the volunteer had been participating in the EMSEMBLE Phase III trial, the last stage of research testing out the vaccine candidate, which uses a weakened version of a common adenovirus as its delivery method. This adenovirus is modified to express a key protein of the coronavirus, hopefully fooling the immune system into building up a defense against the real thing. The dummy virus is also neutered to prevent it from replicating in the human body.
Large clinical trials routinely have safety measures, including temporary pauses, that kick in when someone becomes sick from something that could be related to the experimental treatment. However, this doesn’t necessarily mean that this illness is truly connected to the vaccine. Typically, as is the case here, an independent review board of experts will examine the incident and decide on the next course of action. In its announcement, the company also stated that its own scientists and physicians will also be reviewing the matter.
However, at this point, no further information concerning the patient is being made available.
“We must respect this participant’s privacy. We’re also learning more about this participant’s illness, and it’s important to have all the facts before we share additional information,” the company said.
This isn’t the first pause of a vaccine trial for covid-19. Once in July and once in September, the UK company AstraZeneca paused clinical trials of its candidate, another adenovirus-based vaccine, after two participants developed neurological symptoms. Following an independent review, according to the company, both incidents “were either considered unlikely to be associated with the vaccine or there was insufficient evidence to say for certain that the illnesses were or were not related to the vaccine.” However, though AstraZeneca has since resumed its clinical trials in the UK and elsewhere, it has not received the go-ahead from the Food and Drug Administration to do so yet in the U.S., and outside experts have questioned whether the company has been transparent enough about these adverse events to rule out any possible connection to its candidate vaccine.
Adverse events are entirely expected as part of any large clinical trial and not always caused by the drug or vaccine being studied, and pauses to trials are not necessarily the death knell of an experimental treatment. If anything, these pauses indicate the clinical trial process is working as intended, flagging potential harms before they reach the general public. Whatever ends up happening, it’s a reminder that the road to a successful vaccine for covid-19 will have its bumps and potholes.