The Handelsblatt economic daily reported Monday that Berlin had estimated the efficacy of the jab among over-65s was just 8 percent, citing sources.
The tabloid paper Bild reported that Berlin did not expect the vaccine -- developed with Oxford University and set to get the green light from the EU this week -- would receive a license for use among the elderly, presenting a significant challenge to distribution and vaccination plans in many countries.
"Reports that the AstraZeneca/Oxford vaccine efficacy is as low as 8 percent in adults over 65 years are completely incorrect," the firm said in a statement late Monday.
"In November, we published data in The Lancet demonstrating that older adults showed strong immune responses to the vaccine, with 100 percent of older adults generating spike-specific antibodies after the second dose," it added.
The European Union issued an angry warning to AstraZeneca Monday over its unexpected delay in delivering millions of doses of its Covid-19 vaccine to the bloc.
Last Friday, the pharmaceutical multinational said it would not meet its contractual delivery commitments to the European Union because of unexplained "reduced yields" in its European supply chain.
The European Union has currently authorised two vaccines for widespread distribution, manufactured by BioNTech/Pfizer and Moderna.
The EU is set to add the AstraZeneca vaccine to that list this week, on the understanding that the treatment would be already on hand and available for immediate distribution.
