Health boards told to assume antibody tests do not provide virus immunity
Scotland’s chief medical officer has written to all health boards to say they should not offer “on-demand” antibody testing to NHS staff, care workers or patients.
Dr Gregor Smith said there is insufficient evidence to conclude that people who have recovered from Covid-19 are protected from a second infection.
Currently antibody tests are used in Scotland for surveillance measures to provide population-level information on Covid-19 and these tests will continue to be used in this way. So far 4,431 antibody tests for surveillance purposes have been completed.
Antibodies are made by the body’s immune system as it learns to fight an infection.
Finding antibodies that attack the coronavirus show a person has been infected in the past, but they do not prove they are protected against it in the future.
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.
He gave examples of when an antibody test for Covid-19 could be useful in the clinical management of a patient, for instance when it may be too late in an illness to identify the virus through normal testing but where coronavirus is considered to be a potential cause of their ongoing condition; and linking the inflamatory Kawasaki like syndrome in children to recent Covid-19 as a rising antibody that would indicate a recent infection.
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 UK government bought 3.5 million finger-prick antibody tests in March, but when they were evaluated by scientists in Oxford, they said none of those tested was sufficiently accurate.
Scientists discovered although the tests can show that a person has been infected with a coronavirus, they cannot adequately differentiate between the virus that is causing Covid-19 and other types of coronavirus – which just cause colds.
They found that a range of devices all produced far too many false positives.
Scottish Conservatives health spokesperson, Miles Briggs said: “This is yet another example of SNP Ministers not fully committing to testing during the Covid-19 pandemic.
“The SNP Government is almost half a million tests below the testing capacity in Scotland since the 30th April.
“Carrying out antibodies tests is useful information for people to have, as long as it is made clear that this will not necessarily give immunity and that the you are still able to transmit the virus. If we find out that antibodies do give immunity to Covid-19, SNP Ministers will be on the back foot again, as they have been since the start of the outbreak.”