German biotech CureVac NV said its COVID-19 vaccine was only 47% effective in a late-stage trial, missing the study’s main goal and throwing in doubt the potential delivery of hundreds of millions of doses to the European Union, Report informs via Reuters.

The disappointing efficacy of the shot known as CVnCoV emerged from an interim analysis based on 134 COVID-19 cases in the study with about 40,000 volunteers in Europe and Latin America.

The stakes for CureVac and prospective buyers of its vaccine in Europe had risen after age limits were imposed on the use of the Johnson & Johnson and AstraZeneca vaccines due to a link to extremely rare but potentially fatal clotting disorders.

CureVac’s shot was also expected to help in low and middle-income countries that have lagged far behind richer nations in the global immunization drive.

As CureVac’s only major supply deals, the European Union in November secured up to 405 million doses of the vaccine, of which 180 million are optional. That was followed by a memorandum of understanding with Germany for another 20 million doses.

CureVac’s US traded shares fell 50.6% to $46.81 in after-hours trading following publication of the data.

The company said at least 13 virus variants accounted for the infections among the study population.

Out of the reported COVID-19 cases in the trial, 124 were sequenced to identify the variant causing the infection, it said. One case was attributable to the original version of the SARS-CoV-2 coronavirus that emerged in the Chinese city of Wuhan in late 2019, while 57% of the cases were caused by more highly transmissible so-called variants of concern.

The company added that the interim results suggest the vaccine is effective in younger participants but did not prove efficacy in those above age 60, the age group most at risk for severe COVID-19.

“While we were hoping for a stronger interim outcome, we recognize that demonstrating high efficacy in this unprecedented broad diversity of variants is challenging. As we are continuing toward the final analysis with a minimum of 80 additional cases, the overall vaccine efficacy may change,” said Chief Executive Franz-Werner Haas.