COVID-19 Q&A: Vaccine vs Antibody Test

In our series ‘COVID-19 Explained’, experts from The iQ Group Global demystify frequently asked questions about the COVID-19 virus.  

This week, CRC and Farmaforce Chief Scientific Officer Athena Kolivos explains the difference between a vaccine and an antibody test, and why both are important in the fight against the COVID-19 pandemic. 

What is a vaccine and how does it work?

A vaccine is a preventative biological therapy designed to stimulate an immune response that protects the body against viruses, bacteria or other disease-causing pathogens. It is often made from inactivated antigens. This is the most important part of the vaccine because once the antigen enters the body it stimulates a person’s immune system to make antibodies that fight the antigen and so build immunity, i.e. protection for that individual against getting the infectious disease.

Put simply, when a person is vaccinated against a particular infection, their immune system responds by:

  1. Recognising the invading virus or other germ causing the disease.
  2. Producing antibodies to combat the disease.
  3. Creating a ‘memory’ of how to fight the infection whereby the disease-causing germ is destroyed by the body if exposed to it in the future.

Rather than treating an infectious disease once it occurs, vaccines work to prevent us getting it in the first place.

What is an antibody test?

First off, an antibody is a type of protein the body produces naturally in response to an antigen and is a key part of the body’s immune system. An antibody test usually involves analysing a person’s blood for the presence of a particular antibody or for the amount of antibody present. It’s useful for showing if a person has been infected with a virus or vaccinated against that virus, irrespective of whether or not they showed symptoms of the disease or became ill.  

What does each of them do to treat/prevent the spread of a virus like SARS-CoV-2 that causes COVID-19 disease?

A vaccine is developed to prevent against a particular disease occurring, whereas an antibody test is conducted to detect if an individual has been exposed to the virus or germ causing that disease.

At this stage, much testing is being conducted across the globe to detect the presence of the actual SARS-CoV-2 virus within the body or an immune response to it. There are two types of tests:

  1. Nucleic acid detection tests that detect the presence of genetic material of the SARS-CoV-2 virus causing COVID-19 disease in usually saliva or nasal secretions.
  2. Antibody testing which involves analysing a blood sample to detect specific antibodies IgM and/or IgG and in respiratory infections like SARS CoV-2 IgA which indicates whether a person has been exposed to the virus.

The key difference between these two tests is that nucleic acid testing detects the actual virus being present and can do this early, even before a person develops antibodies and subsequently becomes ill, while the antibody test, to identify certain antibodies shows whether a person’s immune system has started to fight the virus. As it takes time for the body to produce antibodies, a person can have the virus and be spreading the infection to others before their antibodies are detected.  

In the majority of individuals infected with SARS-CoV-2, we would expect to see a peak in viral replication that coincides with the development of symptoms. This is followed by the development of antibodies several days later, known as seroconversion. Testing a patient too early in the course of infection may yield a false-negative result because the patient has not yet seroconverted. Moreover, even when patients have seroconverted, they still may be infectious and continue to shed virus.

There are different isotypes of antibodies, including IgM, IgA, and IgG. Among these, IgG is the best marker to indicate exposure to SARS-CoV-2. The presence of IgG indicates that the patient has been infected with the virus and has mounted an immune response against it. Although the immune response may protect against reinfection, this has yet to be established.

Why are both important? Is one more urgent than the other right now?

Both testing and having a vaccine against COVID-19 disease are important to help stop transmission or spread of the virus among people so it eventually ‘dies’. As a vaccine is still some way off, right now it’s critical that we test early to help confirm, isolate and hospitalise or otherwise treat people with active disease, as well as identify those individuals who may even have no symptoms but can transmit the virus to vulnerable or higher risk people such as the elderly and those with other serious medical conditions.    

Testing is therefore essential from a public health perspective to identify infected people, and decrease the risk of transmission among community and, importantly, to also help healthcare experts and governments understand the extent of the disease outbreak and how it is evolving or changing, particularly in terms of its prevalence, contagiousness and transmission within populations.

Antibodies are key to protecting the body against the disease. When tests show the presence of disease-specific antibodies, that’s evidence of past exposure or infection. Antibodies are an essential part of the immune system that deploys various cells and other components to fight the virus, after which it then has ‘memory’ to recognise and destroy the virus to protect an individual from future disease.

Vaccination is key to stamping out the virus sooner rather than later.

How will both impact the end of the pandemic?

By identifying which individuals have contracted the virus, testing helps to identify, isolate and manage them appropriately so the risk of transmission to others is reduced. This goes a long way to better managing the disease outbreak but may not totally stop its spread.

Vaccination is the ‘holy grail’ to protect people against COVID-19 disease and stop its spread. This is why governments; research institutions and the healthcare industry are pulling out all the stops to have a safe and effective vaccine available around the globe as soon as possible.

Athena Kolivos

Chief Scientific Officer, CRC and Farmaforce

Image sources: Antibody Test ABC, COVID-19 visualisation unsplash-logo
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