Chief Innovation officer
Dr. Yohann White is a medical doctor who focuses on vaccines and conditions affecting the immune system.
I remember getting 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, and 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 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 foreign bodies or 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. Antibodies can come about as a result of catching a germ, and when you recover it usually has learned how to protect you in the future. However, there are some germs that hit you like brand new, and you’re not protected and can become infected again. In some instances, despite the production of antibodies your body is not able to clear the offending agent and disease progresses depending on whether there is effective treatment (e.g., HIV).
Vaccines are another way of triggering the production of antibodies. A vaccine is a harmless part of a germ or weakened form of a germ that is introduced into the body 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.
The way our bodies work is that there is an initial phase where these antibodies are produced, reaching a peak, and then they 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. Although antibodies may stick to a germ and prevent it from latching on to your body or from causing disease, they are not the only means by which your body fights germs. The body also uses immune cells that kill germs by other means. Even when antibodies decrease over time, there are usually antibody-producing cells that get tucked away in certain parts of the body and get called into action the next time you come in contact with such germs.
Does having antibodies equal protection from disease?
The real test of a vaccine is its effectiveness in preventing deaths, disease, and hospitalisation. 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 try to find out what signals, whether levels or type or quality of antibodies or immune cells, correlate with protection from death, hospitalisation or disease, but it is not always easy to figure out. It is unlikely that level of total antibodies is the true signal that equates to protection.
So, should I get a COVID antibody test?
Not surprisingly, a number of manufacturers have come out with antibody tests. But not all antibody tests are equal. 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 persons who recovered from COVID-19) to try to treat persons in hospital with severe COVID-19. In general, the laboratory based tests tend to be more accurate than point-of-care (POC) rapid tests (e.g., finger-prick rapid tests). Also, whereas POC tests tend to 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 before presenting 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 Centers for Disease Control (CDC), US Food and Drug Administration (FDA) and Prevention 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 healthcare professional.