The sprint to find a medical breakthrough to contain Covid-19 stumbled this week, as a pair of pharmaceutical giants working on treatments and vaccines suffered setbacks in the clinic.
On Tuesday, Eli Lilly said enrolment in a government-sponsored clinical trial of its antibody therapy had been halted due to safety concerns. The news came less than a day after Johnson & Johnson (J&J) said research on its experimental vaccine was paused after a study volunteer fell ill.
The developments are likely to heighten worries that the rush to find drugs to prevent and treat infections is moving too fast. Regulators and drug-makers have faced questions on whether political pressure was overwhelming scientific rigour ahead of the Nov 3 presidential election in the United States.
The previous week, US President Donald Trump, trailing in the polls, touted antibody treatments as a cure, and his administration has pushed hard for the rapid approval of the treatments and a vaccine.
But the trial complications are happening in an environment of intense scrutiny, executives and industry observers said, and the highly public nature of the hunt for vaccines and treatments is magnifying events that in other studies would be considered routine.
"I'm not surprised at all that these pauses are happening. Where I would be surprised is if they weren't happening," said Professor Greg Poland, director of the Vaccine Research Group at the Mayo Clinic in Rochester, Minnesota.
J&J's treatment was seen as a front runner in the vaccine race. Along with rival shots by Pfizer and partner BioNTech, Moderna, and AstraZeneca and the University of Oxford, its safety and effectiveness are being studied in a large trial. Hope for its effectiveness is high, as it's expected to be delivered in a single dose. Some rival shots will require another injection.
J&J chief financial officer Joseph Wolk said the firm doesn't know if the person who was sickened had received the vaccine or a placebo. He said J&J is sticking to its development timeline and plans to be able to produce one billion doses a year.
"Everybody is anxious to get a vaccine to the pandemic, for the right reasons," Mr Wolk said. "But nobody is cutting corners or suggesting that there be undue pressure to make that happen."
The stakes in a vaccine trial are especially high, since inoculations are given to people of all ages, several of whom are otherwise healthy.
Prof Poland said he had never seen a vaccine trial under as much scrutiny as Covid-19 trials. "No one wants to misstep... The decisions we're making will affect our children, our parents, our families. We aren't making decisions in a void."
Lilly's drug is part of a class of therapies known as monoclonal antibodies, which top US infectious disease expert Anthony Fauci has called a bridge to a vaccine. Its antibody treatment is similar to one being developed by Regeneron Pharmaceuticals that was given to Mr Trump after he tested positive for Covid-19.
Mr Trump has credited the Regeneron drug for his quick recovery, and has vowed to make it and Lilly's shot widely accessible. This has put a spotlight on both therapies.
"Normally this stuff never makes the news," said Prof Poland. "This is under a microscope and every sneeze and hiccup gets reported."
BLOOMBERG