US drugmaker Johnson & Johnson has paused all trials of its experimental Covid-19 vaccine after one of the participants developed an “adverse reaction”.
It was not immediately clear what caused the reaction in the participant, or whether it was linked to the vaccine, J&J said in a statement, without disclosing further details.
The company last month became the first leading drugmaker to test a single-dose Covid-19 vaccine, as it launched a phase 3 trial that will enlist as many as 60,000 participants across three continents.
J&J’s vaccine is one of several under development, as governments and the pharmaceutical industry race to find one for a pandemic that has killed more than 1m people. Like its UK competitor AstraZeneca, J&J has said it would not seek to make a profit from its vaccine during the pandemic.
In a statement released late on Tuesday, J&J said of the decision to pause the trials that “it’s important to have all the facts before we share additional information”, adding that it is not always immediately apparent whether a participant received the vaccine or a placebo.
The participant’s adverse reaction is being reviewed by an independent data safety monitoring board and the company’s own doctors, said the New Jersey-based drugmaker. It added that serious adverse events are not uncommon in clinical trials, and that their frequency is expected to increase as trial sizes expand.
The company is currently studying its vaccine candidate in one- and two-dose regimens. It is unclear which trial the participant was enlisted in.
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The company said that a pause in a study differs from when a regulator, such as the US Food and Drug Administration, steps in and requires the trial to be halted for a typically longer period. J&J said it does not usually communicate study pauses to the public, though it informs all investigators.
The vaccine J&J is developing uses an adenovirus vector, just like the one AstraZeneca is working on with the University of Oxford. Last month, trials of AstraZeneca’s vaccine were stopped after at least one participant developed unexplained neurological symptoms. They have since resumed, with the exception of the US.
J&J reports its quarterly results later on Tuesday. New York-listed shares were largely flat in after-hours trade.