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Scotland's chief medical officer has said there is insufficient evidence to conclude that people who have recovered from Covid-19 are protected from a second infection.

Dr Gregor Smith has written to all health boards to say they should not offer "on-demand" antibody testing to NHS staff, care workers or patients.

Dr Smith said the tests should continue to be used for surveillance measures.

He said he would keep the advice under review.

Antibodies are made by the body's immune system as it learns to fight an infection.

Finding antibodies that attack the coronavirus show that a person has been infected in the past, but they do not prove they are protected against it in the future.

The main use of the antibody test has been to find out how many people have been infected with coronavirus.

So far 4,431 antibody tests have been completed in Scotland to provide population-level information on Covid-19.

In his letter Dr Smith said serology testing, diagnostic examination of blood serum, could be useful for some patients, for example, when trying to discover if an ongoing condition could have been caused by Covid-19.

But he said: "Having assessed the research available, there is currently insufficient clinical evidence to absolutely conclude that people who have recovered from Covid-19 are protected from either a second infection or from infecting others."

He said that the World Health Organisation had warned about the "potentially negative impacts" on public health if people believed a positive result gave them immunity and led to a change in behaviour.

Dr Smith added: "If clinical evidence around immunity changes we will swiftly roll out a national antibody testing programme in order to realise the potential health, social and economic benefits this would offer, and are preparing now for that prospect."