What’s the Difference Between Antigens and Antibodies?

Both Antigens and antibodies play distinct roles in COVID- 19. COVID-19 Antigens try to damage our health while our Antibodies fight to protect us.

In other words:

COVID-19 antigens are what make you sick, and antibodies are how your body defends against the COVID-19 infection

covid antibody antigen detection time
covid antibody antigen detection time


  • COVID Antigens can be detected earlier than COVID Antibodies.
  • Antibodies can be detected 5 to 7 days after symptoms first appear.

What is an Antibody?

Antibodies are also called immunoglobulins or Ig and there are specific antibodies trained to attack each single type of antigen, keeping them away from your healthy cells and killing these antigens, stopping infection.

The main types of antibodies (immunoglobulins) that you need to understand when reading a COVID test are

  • IgM. These are the first antibodies made by B cells in response to antigens.
  • IgG. These are the most abundant types of antibodies in your plasma. They detoxify harmful substances and provide long-term protection.

 Antibody tests for COVID measure antibodies in the blood. Material for testing is collected by a blood test from drawing blood at your arm or from a finger stick. Depending on which antibodies are being measured, these tests can tell if your body has begun to fight a COVID-19 infection or if you’ve had an infection for a longer period of time.

When testing antibodies for COVID 19:

IgM antibodies are the first antibodies that are made in response to an antigen and the presence of these antibodies will indicate that there is a recent (or still active) COVID 19 infection in the system.

IgG antibodies are created by the body for long term protection from a virus and are produced by the body a while after infection has taken place. The presence of these antibodies will indicate that there was an infection a longer period in the past (or that the subject has taken a Vaccine). These antibodies will stay in the body for a long period of time (science is still determining just how long COVID-19 Antibodies last)

Antibodies may be good for determining if you’ve had COVID-19 for a period of time but may not be a reliable way to tell if you have a current infection. They are also not a reliable way to be sure you do not currently have COVID-19. Additional testing may be needed to exclude an infection.

Antibody tests generally determine if the person has RECENTLY contracted COVID-19ORIf they have EVER had COVID-19 or been vaccinated.

The presence of IgM antibodies will suggest the person still HAS COVID while the presence of IgG antibodies will suggest the person HAD COVID or a Vaccine at some point in the past.

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What Is an Antigen?

Antigens are usually bacteria or viruses, but they can be other substances from outside your body that threaten your health. The COVID-19 antigen is what invades your body and causes you to be sick.

Antibodies to do battle against the disease in an  to the Antigen.

Your body’s response to the invasion of the COVID-19 antigen is to summon your body’s illness-fighting white blood cells, called lymphocytes to make cells called antibodies to fight against the antigens in what is called an immune response.

Relative to testing, Antigen tests  measure antigen proteins from the COVID-19 virus using material collected from your nose or throat. Most rapid COVID-19 tests are antigen tests.

Antigen tests are the tests given to NON SYMPTOMATIC persons to determine if the COVID-19 antigen is present in the body before symptoms present themselves. 

It is important to note that These tests can diagnose COVID-19 but do not absolutely rule out a current, active infection. Only a molecular test at a laboratory can rule out a COVID 19 infection with 100% accuracy.