The world is at risk of losing hard-won gains in fighting Covid-19 as the highly transmissible Delta variant spreads, but WHO-approved vaccines remain effective, the World Health Organisation has said.

Covid-19 infections have increased by 80 per cent over the past four weeks in most regions of the world, WHO director-general Tedros Adhanom Ghebreyesus said. Deaths in Africa — where only 1.5pc of the population is vaccinated — rose by 80pc over the same period.

"Hard-won gains are in jeopardy or being lost, and health systems in many countries are being overwhelmed," Tedros told a news conference.

The Delta variant has been detected in 132 countries, becoming the dominant global strain, according to the WHO.