German biotech CureVac NV said its Covid-19 vaccine was only 47 per cent 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.

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, Reuters reports.

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