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Everyday, more and more Malaysians are getting vaccinated against COVID-19. At the time of writing, 21 million doses have been given; 21.5% of the population has been fully vaccinated and another 22.5% has been vaccinated by 1 dose. (Source: Our World in Data)

As we enter into the new age of virus-human co-existence, more and more people started to ask the question: how long can the vaccine protect us? With the emergence of variants and some individuals getting the infection despite being vaccinated, people are desperate to find ways to measure the protection COVID-19 vaccine offers us. Could an antibody test be the answer?

What’s an antibody test for COVID-19?

Test for both IgG and IgM antibodies. This test was negative. Had it been positive, there would have been two or three lines. Daniel Eriksson, CC BY 4.0 , via Wikimedia Commons

Our immune system consists of an amazing troop of armies equipped with various expertise and weapons. There are two main troops that protect us:

the first-line of defense that is part of the innate immunity and
a highly specialized branch called the adaptive immunity. Unlike the innate immunity, the adaptive immunity can only start to develop after being exposed to a pathogen first, then it may require some time to develop. It’s worth the wait, however, as adaptive immunity provides a long-lasting protection against the particular pathogen (hence it is specialized).

There are a few ways for adaptive immunity to happen, and one way is through the production of antibodies. Antibodies are produced by the B cell after the immune system encounters a pathogen for the first time.

Image credit to https://www.researchgate.net/publication/332777013_Hippo_Pathway_in_Mammalian_Adaptive_Immune_System

To put it into the context of COVID-19, when the SARS-CoV-2 virus enters the body, it will be greeted by the first-line of defense first, meanwhile the B cells are starting to familiarise themselves with the virus. After a few days or weeks, our B cells finally learn enough about the virus and start producing corresponding antibodies (we shall call it COVID-19 antibodies from now on). These COVID-19 antibodies can be detected through an antibody test. If you have a positive test result on a COVID-19 antibody test, it means that it is possible (but not 100% certain!) you were previously infected with the COVID-19.

Do take note that antibody tests cannot be used to diagnose COVID-19. This is because these tests can return a false negative test result even in infected patients (for example, if antibodies have not yet developed in response to the virus) or may generate false positive results (for example, if antibodies to another coronavirus type are detected), so they should not be used to evaluate if you are currently infected or contagious.

A COVID-19 antibody test is different from a COVID-19 antigen test. A COVID-19 antigen test has recently been granted conditional approval by the Ministry of Health for the purpose of self-screening. It works by detecting the molecules on the surface of the SARS-CoV-2 virus. Again, the COVID-19 antigen test is not to be used as a diagnostic test. The diagnosis of COVID-19 should be confirmed only with the gold standard RT-PCR test.

NAAT- nucleic acid amplification test, a.k.a RT-PCR. Image credit: CDC

How does the COVID-19 vaccine work to protect you?

At the time of writing, Malaysia has approved three brands of vaccines: Comirnaty (manufactured by Pfizer-BioNTech), AstraZeneca COVID-19 vaccine and CoronaVac (manufactured by Sinovac and bottled by Pharmaniaga). Comirnaty is a mRNA vaccine; it contains mRNA (i.e. a small part of the genetic sequence of the virus) molecule that can stimulate the individuals’ immunity to produce the specific virus antibodies. On the other hand, AstraZeneca uses a viral vector (think of it like a car) that transports the virus’ antigen code that teaches our immunity to produce antibodies. CoronaVac is an inactivated vaccine, which is a virus that has been killed using high heat, chemical or radiation; such a dead virus still has the ability to stimulate antibody production in our body without causing illness.

Extracted from: https://www.vaksincovid.gov.my/pdf/Program_Imunisasi_COVID-19_Kebangsaan_Versi_Bahasa_Inggeris.pdf, page 13

The takeaway is this: regardless of the brand of the COVID-19 vaccine, they all stimulate our immunity (B cells specifically) to churn out specific antibodies that can fight actual SARS-CoV-2 virus when we’re infected. In other words, vaccines protect us from COVID-19.

So, should you need an antibody test following vaccination?

Let us answer the question we posed earlier: should we test our antibody levels after vaccination? After all, everyone is curious to know how protected we are after getting the jab.

Unfortunately, the U.S. Food and Drug Administration (FDA) does not recommend antibody tests to assess the immunity after COVID-19 vaccination.

This is because of three reasons:

We don’t know exactly how much antibodies are enough to protect you from COVID-19. Let’s say your antibody test result comes back as 80 units/ml. We can’t say for sure that you’ve passed the threshold for protection, or you still lack the minimum amount of antibodies to be protected from COVID-19. More studies are required to better inform the appropriate use of these tests, such as which antibodies may indicate a level of protection that would prevent or reduce the severity of infection or re-infection as well as the duration for which this protection may last. Currently, FDA recommends only healthcare professionals who are familiar with the use and limitations of the test to order the test.
The antibody test may come back as negative even though you’ve been vaccinated. Currently authorized COVID-19 mRNA vaccines induce antibodies to the spike protein and not to nucleocapsid proteins that are likely detected only after natural infections. Therefore, COVID-19 vaccinated people who have not had previous natural infection will receive a negative antibody test result if the antibody test does not detect the antibodies induced by the COVID-19 vaccine.
If the results of the antibody test are interpreted as an indication of a specific level of immunity or protection from COVID-19, people may let their guard down and take fewer precautions against the virus exposure. This may ultimately lead to transmission of the virus.

Don’t let your guard down

Even if you’ve been fully vaccinated, please continue practising all precautionary measures, including mask wearing, washing hands and social distancing. Before scientists understand enough about the virus and its antibody test, we encourage you to take the COVID-19 antibody test results with a grain of salt. It’s best that you consult a healthcare professional before taking a COVID-19 antibody test.

A word from DOC2US

If you have any enquiries related to COVID-19 and its vaccines, you can consult our COVID-19 Task Force, which consists of professional doctors and healthcare professionals, for FREE! You can access free COVID-19 virtual health advisory by downloading the DOC2US app on http://onelink.to/doc2us or use our web chat https://web.doc2us.com/. Alternatively, go to MySejahtera app> Digital Health> Virtual Health Advisory, and click on DOC2US.For more information about COVID-19 vaccination programme in Malaysia, visit https://www.vaksincovid.gov.my/

Disclaimer: COVID-19 is a novel disease. The information and scientific evidence of its development and vaccines are changing as we speak. Some content of this article may be outdated in the future. We encourage you to always speak to a healthcare professional you trust for the latest updates on COVID-19 and its vaccines.

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Cover image credit: Photo by Ivan Diaz on Unsplash