My family and I have had a lot of questions about the COVID test, such as if I take the COVID vaccine and do a test, will it come positive? Well to answer a question like this we need information on how tests work.

Lets start with the basics:

There are two types of molecular tests, antigen tests and nucleic acid amplification tests. Rapid tests are known as Antigen Tests while PCR tests are known as nucleic acid amplification tests. I will talk about PCR tests first. The PCR tests test for DNA. However, the COVID-19 genetic code is actually RNA. So how do PCR tests pick up positive or negative results?

Test de antígenos Covid 3

When your swab of DNA is sent back to the lab, they will isolate RNA and DNA with the process called gel electrophoresis. After isolating the RNA, it is mixed with enzymes (DNA polymerase and reverse transcriptase), DNA building blocks, cofactors, proves and primers. The RNA is transcribed into DNA by the reverse transcriptase. This transcription creates a complimentary DNA. The goal is to isolate the DNA now, and the DNA polymerase does so. The enzyme breaks up the RNA and isolates the complimentary DNA. That DNA is duplicated in order to amplify the molecule. Remember that this DNA is duplicated from the virus RNA.

To amplify the DNA for the equipment to read, the DNA is first heated, denatured, in order to separate the DNA strands. When cooled, primers and probes bind to the DNA strands. The DNA polymerase assembles new DNA strands from the DNA building blocks and when fully reconstructed, it has been successfully amplified. This is done repeatedly with the RNA and thus, creates many complimentary DNA’s ready to amplify.

If SARS-CoV-2 complementary DNA is present in the sample, primers copy the infected regions while probes, signaling proteins, stick to it and release a visual signal read by the equipment. Because there are millions of amplified DNA, there will be lots of signals being produced by the probes. If their is no virus, the probes do not stick and this no signal release and a negative result shows. Thanks to the power of signaling and cell communication, lab instruments can pick up on it and give us a positive or negative result.

The rapid test works in a very different way. Antigen rapid test takes about 15 minutes. The goal is to detect the spike protein of the coronavirus. The liquid drops onto the droplet. Antibodies are on the test pad, with three sets.

The testing pad, we’ll call pad, consists of the location for liquid drops, and a C and T line. At each segment of the pad there are different antibodies. Those antibodies will bind to the spike protein as well as the other antibodies. When the liquid is dropped in, capillary flow allows the liquid to move down the pad. The first antibodies will attach to the virus, which then move down the pad. Then the antibody will bind to primary and secondary antibody, not the virus. The combining of antibodies create the line which results in the positive or negative outcome.


To answer my question, no. The PCR and rapid tests should not test positive if one has taken the vaccine recently. This is because both tests are checking for active viruses and polymerase. Not immunity.


If you feel any symptoms take a rapid test, sometimes it comes negative when you really have COVID and that’s because at the early stages of COVID development in the body, there will not be enough active viruses going around.  But that does not mean you are not contagious, please be safe and stay healthy!