Shares in the French and British pharma firms dived Friday, after they said initial trials of their vaccine had generated an insufficient immune response in older adults. They said they were still confident that the vaccine would pan out but—pending successful improvements—its availability is now only penciled in for Q4 next year.

Sanofi’s share price fell more than 2% on the news, while GSK was down more than 1.4%, underperforming the wider European markets.

Friday’s announcement is a blow for those hoping to vaccinate the planet as quickly as possible.

Despite the fact that Pfizer and BioNTech’s COVID-19 vaccine is already being deployed in the U.K., and although Moderna’s candidate has shown very promising results, a multitude of vaccines will be needed to complete the task.

Sanofi and GSK are among the participants in the U.S.’s Operation Warp Speed vaccine-development program; the Trump administration pledged $2.1 billion for 100 million doses of their shot. The European Union has an order in for 300 million doses. Both will have to wait.

“The results of the study are not as we hoped,” said GSK vaccine chief Roger Connor in Friday’s statement. Sanofi Pasteur executive VP Thomas Triomphe said the companies were disappointed, but “all our decisions are and will always be driven by science and data.

“We have identified the path forward and remain confident and committed to bringing a safe and efficacious COVID-19 vaccine,” said Triomphe. “Following these results and the latest encouraging new preclinical data, we will now work to further optimize our candidate to achieve this goal.”

Sanofi/GSK’s candidate should carry the advantage of not requiring extra-cold refrigeration, as Pfizer/BioNTech’s does. This is a characteristic shared by candidate vaccines from Johnson & Johnson and AstraZeneca, which are seen as crucial to the success of Operation Warp Speed.

AstraZeneca’s candidate, which was developed alongside the University of Oxford, has puzzled many observers by proving more effective when the first of its two doses is only a half-dose. The British company is now planning to conduct new trials in order to figure out what’s going on.

Meanwhile, also on Friday, the Australian biotech firm CSL and the University of Queensland halted trials of their candidate vaccine, and the Australian government canceled its order for 51 million doses. Part of the vaccine was made from the human immunodeficiency virus, and some trial participants got false positives in HIV tests.