What is an antibody test?
There are two types of tests when it comes to the coronavirus; the first kind is diagnostic, which can tell you whether you have the coronavirus at the time of being tested, and there's a short window of time after first showing symptoms during which it is effective.
The antibody test is different, and can show you whether you have previously been infected with the virus and have since recovered. Also known as a serology test, it's a blood test that tells you whether you have antibodies – proteins that fight off specific infections.
What does it mean if I test positive?
If you have the antibody, it means you have been infected with the coronavirus and that your immune system produced this protein in order to fight off the virus.
Antibodies often mean you are immune from the particular virus they developed to protect you from. But scientists still don't know if that's the case with the coronavirus, because it's a new disease. So researchers are working to find out if having the antibody does provide you with immunity, and if so, what level of immunity and for how long.
Here's what Sweden's first coronavirus antibody tests tell us
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Antibody tests being carried out in a Stockholm conference centre. Photo: Emma-Sofia Olsson /SvD/TT
How can I get an antibody test in Sweden?
There are a few different routes. You may be referred for an antibody test by your doctor, if they want to rule out whether you've had the coronavirus.
A small number of people have been sent home-testing kits in the post to take part in a random study, and there may be further tests like this in future, but as the studies are randomised, there is no way to apply to take part.
If you work in the healthcare sector or work in or are resident at a care home, you may be offered the test for free. The goal of this is to allow more healthcare staff to go back to work when it's safe for them to do so, and to help risk planning and prevention in these high-risk environments.
One of the largest companies offering the tests is Werlabs, which offers tests for free to healthcare workers, and has also offered paid testing to several large companies including Spotify, H&M and Tele2 in Stockholm.
Werlabs is also offering the tests to private individuals in 14 towns: Stockholm, Göteborg, Malmö, Ekeby, Halmstad, Jönköping, Kristianstad, Mariestad, Strängnäs, Trollhättan, Ulricehamn, Visby, Vetlanda, Västerås. You can order the tests online, go to a testing location to have the blood test, and then receive your results in two to four days. The cost is 750 kronor.
It's also possible to buy antibody tests as an individual from other private care companies, such as Hedda Care which charges 950 kronor per test, but many of these tests have been criticised as unreliable.
The current advice in Sweden is to avoid taking the antibody tests as an individual if you are not referred for one by your doctor or workplace, because there's a risk of false positives.
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Who can take the antibody test?
According to Werlabs, you must have been completely free of symptoms before taking the test in order to get an accurate result.
The Public Health Agency has said it takes three to four weeks in order to develop antibodies to the virus, so if you take it too soon after infection, you won't get a positive result even if you've had the virus.
The agency also currently advises individuals against taking the tests with the aim of informing personal decisions about safety and risk-level. This is due to the risk of false positives. It does however say that tests can be useful for companies, in order to get a more general overview of the level of infection within their company to prioritisation and allocation of resources
When will they be available for everyone in Sweden?
Scaling up antibody testing is a goal that the authorities are working towards, according to Health Minister Lena Hallengren and Public Health Agency general director Johan Carlson. But there's no clear time frame, since they have both said the crucial thing is first to ensure a high level of accuracy in the tests.
File photo: AP Photo/Damian Dovarganes/TT
How reliable are they?
It depends on the test. Unreliability has been one of the main reasons why they have so far been used only on a small scale.
Werlabs, one of Sweden's largest blood test providers, claims the tests have 99.6 percent specificity and are 100 percent sensitive, meaning that if the antibody is in your blood, the test will detect it, but if you do not have the antibody, there is a 0.4 percent chance of false positives. Even this small figure means there's a chance people will put themselves at risk believing they may have immunity.
This uncertainty along with the general uncertainty around possible immunity are two reasons why even if you test positive for the coronavirus antibody, it doesn't necessarily mean you're safe from reinfection and can resume life as normal.
So why are they important?
There are two reasons. Firstly, understanding how many people have had the coronavirus will help give clearer information about how widely the virus spreads and how deadly it is.
Secondly, the World Health Organisation says it is likely that the antibody will provide at least some protection from re-infection. The details on that aren't clear yet, but if research shows that people with the antibody are immune, this will mean those people can go back to work and resume other parts of life, and the more people in society who we know are immune, the more that the general risk of infection will be reduced.
What do I do if I think I've had coronavirus but haven't had a test?
You shouldn't change your behaviour. That means continuing to take the same precautions that are currently recommended, including keeping a two-metre distance from others in public, limiting unnecessary social contacts, working from home if you can, and staying at home completely if you have any cold- or flu-like symptoms. A lot of illnesses have similar symptoms to the coronavirus, so without a test it's impossible to know if you've had it, and even if you have, full immunity is not guaranteed.
There is some evidence suggesting that people can experience symptoms from coronavirus over a long time period, so if you experience concerning symptoms or aren't seeing an improvement, contact a medical professional and seek advice.