What’s the latest on coronavirus antibody tests?

A new test to determine if someone has been infected with coronavirus has been released onto the market.

According to its developer, Swiss pharma giant Roche, the antibody test “has a specificity greater than 99.8% and sensitivity of 100%”, pinpointing antibodies to COVID-19 present in blood samples.

Antibody tests – which check the blood for the proteins produced by our bodies’ immune systems to fight infections – have been identified by a number of countries as key to tackling the spread of the virus and loosening lockdowns, as they can show who has been exposed to the disease even if they had been asymptomatic.

After independent testing by Public Health England found the Roche test to be highly specific and accurate it became the first coronavirus antibody test approved in the UK. A second test, from Abbott Laboratories, has since also been approved in the UK. Both also have approval for use from the US Food and Drug Administration.

How does it work?

Unlike swab tests, which indicate whether a person has coronavirus at the point they were tested, blood-based antibody tests can show whether or not someone has been infected in the past.

The Roche test and others like it rely on a machine to identify the presence of antibodies against the virus that causes COVID-19 – SARS-CoV-2 – in blood samples. It identifies antibodies from at least 14 days after infection. And the test is specific for this strain of coronavirus – so it won’t be confused by antibodies to other coronaviruses, such as the common cold.

It is a different type of test to the home finger prick blood tests which have also become available. There is still hope that such finger prick tests could help provide rapid results, but there have been some concerns over their accuracy.

What does a positive result mean?

Widespread use of such tests will tell governments what proportion of the population has had COVID-19, and better understand how it has spread.

But the World Health Organization has warned against using the results of diagnostic tests for "immunity passports" that would enable individuals to travel or return to work. The body is concerned about the accuracy of some tests available and points out there is still a lot of uncertainty around the degree of protection past infection gives.

People who assume they are immune to a second infection because they have received a positive test result may end up ignoring public health advice, it says.

There is also concern that such passports could lead to discrimination, creating a divide in society with, for example, employers favouring those who could prove previous infection.