Illustration of the AdVac^® adenovirus technology, being tested by  Johnson & Johnson, (Credit: J&J)

Johnson & Johnson, the only pharma firm currently developing a one-dose COVID-19 vaccine candidate, has “paused” its Phase 3 clinical trial due to an unexplained illness in one of the participants. A press release issued on Monday confirmed reports that a safety monitoring board had been convened to review the event and related data, but gave no further details about the nature of the illness.

Meanwhile the New York Times reported that Eli Lilly had also paused its clinical trial testing an antibody cocktail treatment for COVID-19 on hundreds of hospitalized people, due to a safety concern. The drug is simlar another antibody cocktail given to President Trump after he was diagnosed with Covid-19 earlier this month. Trump had pronounced the cocktail that he received, developed by the pharma company Regeneron, as a “cure,” and said he wanted to make it widely available for free to hospitalized COVID patients.  A few days later, Regeneron as well as Eli Lilly applied for Food and Drug Administration Emergency Use authorizations, even though the trials of the treatments were still underway.

In terms of the vaccine trial, J &J said that its pause in the vaccine clinical trial was “temporary”, not unusual when unexplained illnesses occur, and represented the high degree of concern with safety.

“We have temporarily paused further dosing in all our COVID-19 vaccine candidate clinical trials, including the Phase 3 ENSEMBLE trial, due to an unexplained illness in a study participant. Following our guidelines, the participant’s illness is being reviewed and evaluated by the ENSEMBLE independent Data Safety Monitoring Board (DSMB) as well as our internal clinical and safety physicians,” said the statement.

The announcement is significant, however, because the J&J vaccine is the only candidate being tested  that would presumably confer immunity with just one vaccine dose. The three other leading vaccine candidates now in Phase 3 trials by AstraZeneca, Pfizer and Moderna, all require two doses.

Along with the ease of distribution offered by a one-dose vaccine, the other advantage of the J&J canadidate is that the vaccine can be stored for at least three months at t 2-8° C – meaning that the vaccine would not require the special cold storage infrastructure that other vaccine candidates would need.

Like the AstraZeneca vaccine, the J&J candidate works by using an adenovirus as a vector (a carrier) of an antigen’s genetic code, to mimic components of the SARS-CoV-2 virus without causing severe disease, in a patented  AdVac^® technology. The technology  also being tested in a J&J clinical trial of a vaccine against Ebola. The Astra-Zeneca vaccine was also been paused in the United States after two trial participants developed side effects, reported to be a rare form of spinal inflammation, myelitis.

In contrast, neither the Pfizer nor the Moderna vaccines so far have suffered significant interruptions.  Both companies are using a different, mRNA technology that uses an RNA fragment of the COVID-19’s characteristic spike to teach the body to mount an immune response. And in fact both companies recently said that they are on track to present the results of their Phase 3 clinical trial to the US Food and Drug Administration this fall,  later this month, in the case of Pfizer, while Moderna has said that it would present its results in late November.

The J&J Phase 3 trial started only on 23 September, late in comparison with other front-runner candidates where trials started over the summer.  But with an enrollment goal of 60,000 people on three continents, it was by far the largest trial of a vaccine candidate so far, and the one-dose regime appeared to give it a shot at rapidly yielding results.  Now those hopes appear to have been suspended, along with the trial.

Image Credits: Johnson&Johnson.