According to a study conducted by the American group on a small group of eight people who received the vaccine produced by Janssen, the group's pharmaceutical company, antibodies and immune system cells neutralised the Delta variant.

A second study involving 20 patients vaccinated at the Beth Israel Medical Centre in Boston, USA, produced the same results.

Data from the studies has been uploaded to the BioRxiv scientific article "pre-publication" platform, where scientists can submit their work prior to possible publication in a scientific journal.

"We believe our vaccine offers long-lasting protection against Covid-19 and enables neutralisation of the Delta variant," Paul Stoffels, chief scientific officer at Johnson & Johnson, said, quoted in a statement.

Data studied over eight months show that the single-dose vaccine developed by the laboratory "produces a strong neutralising antibody response," said Mathai Mammen, head of Research and Development at Johnson & Johnson.

The World Health Organisation (WHO) warned on Thursday, 1 July, of the risk of a new wave of the pandemic carried by the Delta variant in Europe.

This variant, initially detected in India, is 40 percent to 60 percent more transmissible than Alpha, according to the WHO.

The WHO reiterated that the vaccines are effective against the Delta variant, but it is necessary to receive both doses, not just one.

The Delta variant of the coronavirus, which is particularly contagious, is expected to account for 90 percent of new Covid-19 cases in the European Union by the end of August, the European Centre for Disease Prevention and Control (ECDC) estimated last week.