The participant’s illness is being evaluated, the New Brunswick, New Jersey-based company said late Monday, adding that it would share information after further investigation. J&J shares fell 2.4% in trading before U.S. exchanges opened. The vaccine is undergoing tests in as many as 60,000 volunteers from Peru to South Africa.

J&J is racing along with rivals such as Moderna Inc., Pfizer Inc. and AstraZeneca Plc to deliver a shot to help blunt the pandemic. Drugmakers must balance time pressures—especially as coronavirus cases set new records—with safety considerations in the crucial last stage of testing.

“We’re going to have to get used to hearing these sorts of reports of pauses,” Hassan Vally, an associate professor in epidemiology at La Trobe University in Melbourne, said by email. “As you vaccinate more people in these trials the chances are that there will be some illnesses in participants. The only difference here is that in the world that we live in right now, the progress of these trials are in the public eye, and so we are riding every bump.”

British drugmaker Astra last month temporarily stopped tests of its own vaccine candidate after a trial participant fell ill. That study has resumed in a number of countries, but remains halted in the U.S.

While such pauses are routine in the pharmaceutical industry, J&J’s interruption may contribute to concerns over safety with vaccine research progressing at an unprecedented pace. Developmental processes that usually take years have been compressed into months, egged on by politicians wanting a solution to a pandemic that has killed over 1 million people and scuppered economic growth.

“We are committed to providing transparent updates throughout the clinical development process of our vaccine candidate,” J&J said in a statement. “Adverse events – illnesses, accidents, etc. – even those that are serious, are an expected part of any clinical study, especially large studies.”

In recent days, officials have sought to dampen expectations for a quick fix. Guido Rasi, executive director of the European Medicines Agency, said last week that a vaccine was looking unlikely by year end. The U.S. Food and Drug Administration plans to demand two months of safety data before reviewing any application and said any shot submitted will need to be evaluated by an independent panel.

J&J executives will likely face questions about the trial pause Tuesday morning when they present third-quarter earnings. Representatives for the FDA could not immediately be reached by phone or email for comment after business hours.

Safeguards in Place

The pause “is good news in that it demonstrates that the regulatory safeguards to protect the public are still in place,” said Michael Kinch, a vaccine specialist and professor at Washington University in St. Louis. He said more information is needed to determine whether the issues with J&J’s vaccine are related to the illness experienced by Astra’s trial participant.

In the Astra incident, a patient who received the vaccine experienced unexplained neurological symptoms, prompting a halt in early September. Though trials have since resumed in the U.K., Brazil and South Africa, work remains paused in the U.S., raising questions over whether regulators there have lingering safety concerns.

J&J’s setback will add to these worries, delivering another reality check as some politicians continue to say that a Covid-19 fix is around the corner.

The pursuit of a vaccine has become a political topic, with some observers concerned that U.S. President Donald Trump’s eagerness to see a shot authorized before the election could compromise the scientific process.

Higher Bar

An inoculation must clear a higher bar than a treatment because it’s injected into healthy individuals. Public trust in a vaccine will be crucial as health authorities try to convince millions around the world to take it. Drugmakers have condensed the development timeline substantially, but are eager to avoid the perception that they are bending to political interference and have pledged to avoid scientific shortcuts.

While there are hundreds of Covid-19 vaccines being developed around the world, J&J is among a small group of vaccine makers which have progressed into final-stage human studies. The company is dosing up to 60,000 volunteers in the first big trial of an Covid-19 inoculation that may work after just one shot.

J&J Chief Executive Officer Alex Gorsky joked in an interview earlier this month that he’s asked “almost every 15 minutes” when a vaccine will be available. At the time, he reaffirmed J&J’s expectation that by “late this year, early next year,” the company could begin reviews with regulators for possible emergency use authorization. That timeline may now be in question.

Astra, Pfizer and Moderna are among other western developers with late-stage clinical trials. Pfizer has said it could have the data to support an application for an emergency authorization as soon as this month. Moderna doesn’t expect to have such data until late November.

Russia has tried to leapfrog the process in the race to be first with a Covid-19 shot, approving its Sputnik V product before it’s undergone full testing, drawing widespread skepticism. China also has several candidates in the works and the country’s top bio-safety scientist said last month that shots will be ready for public use as early as November or December.