Pfizer and BioNTech have said they will seek authorisation for a third dose of their Covid-19 vaccine to boost its efficacy as the Delta variant drives devastating outbreaks in Asia, including in Thailand where fresh curbs have been announced.

The companies said on Thursday they expected that a third dose will perform well against the strain, and that they would be seeking authorisation in the United States, Europe and other regions in coming weeks.

Initial data from an ongoing trial showed a third shot pushed antibody levels five to 10 times higher against the original coronavirus strain and the Beta variant, first detected in South Africa, compared with the first two doses alone, according to a statement.

The companies said they expected similar results for Delta — but added they were also developing a vaccine specifically tailored to fight the deadly strain.