BUDAPEST (BLOOMBERG) - The Chinese-made Sinopharm Covid-19 vaccine has failed to produce sufficient antibodies in a quarter of elderly people who were voluntarily tested in Budapest, according to a study by the opposition-led Budapest City Hall.

The results were published just as Hungarian Prime Minister Viktor Orban's government, which has faced opposition criticism for having widely administered Sinopharm shots to older people, started offering third shots this week for anyone who requests them.

Hungary, which has had the highest level of Covid-19 deaths per capita after Peru, is the only European Union country to have deployed the Sinopharm vaccine to combat Covid-19.

The non-representative study tested 13,524 people who were at least 60 years old. More than half had been inoculated with Sinopharm.

The results showed that 25.9 per cent of those people did not have the minimum antibody level of 50 AU per millilitre, compared with 3.2 per cent for those who received Russia's Sputnik V, 1.6 per cent for Pfizer-BioNtech and 1.1 per cent for Moderna.

Sinopharm's ability to generate antibodies got progressively worse with age, with vaccinated people who did not have the minimum antibody level rising to 34.5 per cent among those aged 80 and over, the results showed.

Mr Orban's government cited the initial slow pace of procuring Pfizer's and Moderna's vaccines for buying the shots from China and Russia. The country has also used the AstraZeneca and Janssen vaccines.