SCOTLAND’s chief medical officer has told health boards to assume that antibodies do not protect against coronavirus until more evidence is available.

Dr Gregor Smith has written to all Scottish NHS boards, warning that there is currently insufficient evidence as to how much protection antibodies give people – as well as the length of time any protection lasts.

Dr Smith has also warned that the only clinically safe option is for health officials to assume no meaningful immunity from a positive result until there is scientific evidence to suggest otherwise.

Antibody tests are currently used in Scotland as surveillance measures as part of estimates of population-level information on Covid-19. So far, 4,431 antibody tests for surveillance pruposes have been completed.

Dr Smith 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.

“Until such evidence exists, the main public health benefits are for research purposes or in the clinical management of patients.

“The World Health Organisation and SAGE have warned there are potentially negative impacts on public health if individuals assume immunity from a positive result and adapt their behaviour in a way which could increase the risk of continued transmission.”

He added: “On this basis, advice to health boards is not to offer on-demand antibody testing.

“Our approach is being kept under ongoing review. 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.”

The warning comes amid reports that a staff member at Home Farm care home on Syke, where a Covid-19 outbreak killed 10 residents after 63 people were infected, who had previously tested positive and recovered has tested positive again.

The reports were made public by Ross, Skye and Lochaber MP, Ian Blackford.

The home's operator, HC-One, said they had been told by public health experts that the positive test is "likely as a result of the original infection and not due to a reinfection".

Writing on Twitter, the SNP leader at Westminster, said: “One of the staff members at Home Farm who had previously tested positive for Covid-19, recovered and was tested negative twice has tested positive again.

“The staff member concerned was re-rested on Sunday and received confirmation last night that they were positive. It is important to stress that when someone does test positive having previously had Covid-19 that they may not necessarily be infectious.”

He added: “Clearly however we cannot take any risks. I have been in touch with NHS Highland this morning and I have asked that as a precaution all staff and residents at Home Farm are tested today and the results must be known ahead of the court hearing tomorrow.

“I felt it important that the public were aware of this development but I do acknowledge the work that is ongoing to deliver effective infection control at Home farm.

“I am sure that all in the community will want to offer full support to the residents, their families and all staff at what has been a distressing time for all.”

A spokesman for HC-One said: “We have been assured by public health experts that the positive test returned recently from a Home Farm colleague is likely as a result of the original infection and not due to a reinfection.

"This means that the risk of transmission from this person is very minimal.

"However, we are of course working closely with our local health and care partners and are taking all appropriate steps to respond to this.

"Testing is being made available to everyone who has entered the home recently and will be completed as a matter of urgency.

“Home Farm has had the highest standards of infection control over recent weeks, working in partnership with and overseen by colleagues from the NHS, and we are confident we have done all we can to support this home in its recovery.

"There had been no new Covid cases at Home Farm for 33 days, prior to the result on Sunday, and we hope the current round of testing will show there has been no further transmission.”