Should I get a COVID antibody test?Sunday, September 05, 2021
Dr Yohann White
I remember a telephone call from a doctor who had recently had a COVID antibody test that was negative, despite having had confirmed COVID-19 and having been vaccinated sometime after. Her expectation, naturally, was that she would have had antibodies. She was, understandably, concerned that she may still be vulnerable to getting COVID-19.
In other situations, patients with certain medical conditions that make their immune systems work below the optimal level asked about how they could confirm whether they had mounted an adequate response after getting the vaccine against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the novel coronavirus disease 2019 or COVID-19. Others who had recovered from COVID-19 wanted to know if they were already protected or whether they should get the vaccine.
What are antibodies?
Antibodies are substances made by the body to fight germs; anti- means against, and -body refers to things that your body doesn't quite recognise. These antibodies are your body's way of learning to recognise germs and putting up a fight to protect you from disease. Vaccines trigger the production of antibodies.
A vaccine is a harmless part of or weakened form of a germ given, in very small amounts, to train your body to recognise a germ and put up a fight should you come in contact with that germ in the future. There is an initial phase where these antibodies are produced, the levels then reach a peak and then decrease over time. Antibodies may take a week or more to develop after infection and so are not good at telling if you have a current infection. Similarly, antibodies take about two weeks to develop after vaccination. The body also uses immune cells that kill germs by other means. Even when antibodies decrease over time, there are antibody-producing cells that get tucked away in the body and spring into action the next time you come in contact with that germ.
Does having antibodies equal protection from disease?
The real test of a vaccine is its effectiveness in preventing deaths, hospitalisation and severe disease. The amount of antibodies elicited by a vaccine may or may not equate to degree of protection. Antibody levels are easy to measure because all you need is a small amount of blood and relatively simple tests, so these are the things that get measured the most by vaccine manufacturers.
Measuring other aspects of the immune response is more labour-intensive and usually requires more blood and other types of body samples. Researchers are trying to find out what signals — whether levels or quality of antibodies or immune cells — correlate with protection, but it is not always easy to figure out. It is unlikely that just level of total antibodies is the true signal that equates to protection.
So, should I get a COVID antibody test?
Not all antibody tests are equal. Some antibody tests are designed to detect antibodies resulting from natural infection but not from vaccination, and vice versa. The University Hospital of the West Indies (UHWI) has validated antibody tests and has even published scientific papers on the subject. These validated tests have also been an important tool in an ongoing research study at UHWI using convalescent plasma (blood donated from people who recovered from COVID-19) to treat individuals in hospital with severe COVID-19.
In general, the laboratory-based tests tend to be more accurate than point-of-care (POC) tests (for example, finger-prick rapid tests). Whereas POC tests give a positive or negative reading, lab-based tests usually give a value that roughly corresponds to the level of antibodies in the blood. Antibody tests have also been useful in situations where patients with COVID-19 take a long time to come to hospital, and at which time molecular or antigen tests may be negative, and the antibody test may be the test to clinch the diagnosis of COVID-19. However, in terms of trying to confirm whether you are protected after recovering from COVID-19 or after vaccination or because you are immunocompromised, the US Food and Drug Administration (FDA) and World Health Organisation (WHO) do not recommend routine COVID antibody testing at this time.
Should you have an antibody test done, you should discuss the results with a qualified health care professional.
Dr Yohann White is a medical doctor focusing on the immune system and vaccines. Visit Para Caribe Consulting's website at ParaCaribe.com or on social media @ParaCaribeJA. Also, e-mail Dr White at email@example.com
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