The World Health Organisation chief has warned against suggestions by some to just allow Covid-19 to spread in the hope of achieving so-called herd immunity, saying this was “unethical”.

“Herd immunity is achieved by protecting people from a virus, not by exposing them to it,” Tedros Adhanom Ghebreyesus said.

“Never in the history of public health has herd immunity been used as a strategy for responding to an outbreak, let alone a pandemic,” he insisted.

Relying on naturally obtaining herd immunity in such a situation would be “scientifically and ethically problematic”, Tedros said. “Allowing a dangerous virus that we don't fully understand to run free is simply unethical. It's not an option.”