WASHINGTON - Pfizer and BioNTech announced Monday that their coronavirus vaccine may be more than 90 per cent effective, after the two pharmaceutical firms released interim data from their ongoing large-scale trial.

Preliminary analysis, conducted by an independent data monitoring board, looked at 94 infections recorded so far in the vaccine’s phase 3 study, which has enrolled nearly 44,000 people in the US and five other countries.

Of those participants who were infected with Covid-19, it is currently unclear how many had received the vaccine versus those who had been given a placebo.

An analysis of its coronavirus vaccine trial suggested the vaccine was robustly effective in preventing Covid-19, a promising development as the world has waited anxiously for any positive news about a pandemic that has killed more than 1.2 million people.

The longevity of the immune response provoked by the mRNA-based vaccine also remains unknown.

However, the findings are the most promising indication to date that a vaccine will be effective in preventing disease among infected individuals, handing humanity a crucial tool in tackling the pandemic.

Pfizer and its German partner BioTech will continue with the phase 3 trial until 164 infections have been reported among volunteers - a figure that will give regulatory authorities a clearer idea of the vaccine’s efficacy.

This number is expected to be reached by early December in light of the rising US infection rates, Pfizer said.