WASHINGTON - US pharmaceutical giant Johnson & Johnson sought Tuesday to reassure investors after its stock slumped on an announcement that it was pausing a Covid-19 vaccine trial over a sick participant.

The company is one of several working on a vaccine, but on Monday it announced the unexplained illness, closing enrollment for the 60,000-patient trial while an independent patient safety committee is convened.

The announcement sent shares tumbling 2.3 percent at the close of trading Tuesday, even as the company reported healthy third-quarter results, with sales growing 1.7 percent to $21.08 billion.

In a conference call earlier in the day, J&J's global research head Mathai Mammen said "our plan is to continue the study" following "a temporary pause" caused by the illness.

"It's not at all unusual for unexpected illnesses (to occur) in large studies over their duration. In some cases, serious adverse events... may have something or nothing to do with the drug or vaccine being investigated," he said.

• J&J pauses COVID-19 vaccine trials due to unexplained illness in participant

The Phase 3 trial had started recruiting participants in late September, with a goal of enrolling volunteers across more than 200 US and international locations, the company and the US National Institutes for Health (NIH), which is providing funding, said.

The other countries where the trials were taking place are Argentina, Brazil, Chile, Colombia, Mexico, Peru and South Africa.

The company's chief financial officer Joe Wolk said it was unclear whether the participant who became ill was receiving the trial vaccine or the placebo.

"We are waiting for the independent drug safety monitoring board to do their analysis," he said.

J&J is one of 11 organizations globally to begin a Phase 3 trial on a Covid-19 vaccine.

Washington has given the multinational about $1.45 billion in funding under Operation Warp Speed.

The vaccine is based on a single dose of a cold-causing adenovirus, modified so that it can no longer replicate, combined with a part of the new coronavirus called the spike protein that it uses to invade human cells.

© Agence France-Presse