Pfizer and BioNTech are preparing to start clinical trials of a version of their Covid-19 vaccine targeting the Delta variant next month, amid fears that existing jabs will offer less protection against the infectious strain spreading quickly across much of the world.

The drugmakers were developing an updated version of their existing vaccine that would be made using the lineage of the Delta variant, Pfizer said on Thursday. Pfizer and BioNTech are in discussions with the US medicine regulator to finalise their clinical trial plans and expect to begin studies in August.

The companies are the first to create a vaccine focused on targeting the Delta variant, a move that underscores concerns that the highly transmissible strain may be able to evade existing jabs and new measures will be needed to tackle it.