[ad_1]
After getting a Covid antibody test in July after my Covid illness in early February, I was surprised to find that I had antibodies six months after my infection.
No one knows how long Covid antibodies last, so in September I had a new test. He still had antibodies. In mid-October, same result.
Well, good for my immune system, but it doesn’t mean I’m immune to Covid so I’m still protecting myself.
I believe, like many scientists, that the antibody test is ideal for identifying people who have had Covid.
Jessica Watson and her colleagues at the Universities of Oxford and Birmingham at the BMJ claim that testing for antibodies in people with and without symptoms would track the spread of current and past infections.
(Image: Getty)
This would provide invaluable information on where the virus is, where it is moving, and where it is likely to wreak havoc.
So what kind of antibodies do we test? We produce three main types of antibodies in response to infection: IgA, IgG, and IgM.
IgM appears first and disappears quickly. IgG and IgA persist and often reflect a longer-term immune response.
Antibody tests look for changes in the level of these antibodies through a blood sample from a vein or a skin prick.
The main tests currently in use in the UK are the Abbott Assay, which detects IgG, and the Roche Assay, which detects both IgM and IgG.
We are all concerned with the accuracy of antibody tests, and as Jessica Watson and her colleagues point out, the timing of a test is crucial.
It turns out that the maximum accuracy for the combined IgG or IgM tests is 96% on days 22-35 after the first symptoms.
For IgG alone, the maximum precision is 88.2% between days 15 and 21 after the onset of symptoms.
There is no point in testing for antibodies too soon after the disease begins.
The immune system takes time to recognize the virus and make the antibody, a complicated job.
And if we are lucky, the immune system will form a memory so that immunity will last and protect it in the future.
Even with this high precision, many tests are likely to give false negatives.
Therefore, a negative test should be challenged if a person has typical symptoms. False positives are rare: less than 2% of people who have not had Covid-19 will have a false positive test.
But a truly positive test should not be taken as protection against the virus and precautionary measures such as social distancing should be maintained.
[ad_2]
