Your Covid-19 questions answered

I’ve just been vaccinated, so why did I test positive for Covid-19?

15 September 2021 - 07:00
The vaccine cannot cause a positve Covid-19 test result. Stock photo.
The vaccine cannot cause a positve Covid-19 test result. Stock photo.
Image: 123RF/MILKOS

You recently received the Covid-19 vaccine but take a test and find you are positive for the coronavirus. What happened?

According to the National Institute for Communicable Diseases (NICD), a division of the National Health Laboratory Service, “the vaccine will not cause a positive Covid-19 test result”.

Instead it suggests that person was most likely in the incubation period of Covid-19 infection when they were vaccinated.

“This is especially true when infection rates are high,” said the NICD.

This was seconded by the US Centers for Disease Control and Prevention: “None of the authorised and recommended Covid-19 vaccines cause you to test positive in viral tests, which are used to see if you have a current infection.​

“If your body develops an immune response to vaccination, which is the goal, you may test positive in some antibody tests. Antibody tests indicate you had a previous infection and you may have some level of protection against the virus.”

It also typically takes two weeks after vaccination for the body to build immunity against Covid-19.

While it may be alarming, Dr Marlin McKay told TimesLIVE there is nothing to worry about if you take the vaccine without realising you have Covid-19, especially if you are asymptomatic. 

“If you are symptomatic, if you have any symptoms, whether you think it is Covid-19 or not, wait until you are better. If you have been exposed to someone with Covid-19, also rather wait,” he advised.

The NICD also noted that some may experience a false negative or false positive test result.

“The amount of virus in your body, which is called the viral load, changes during the course of an infection, starting from low levels which increase over a few days and then start to decrease towards the later stages of infection,” it said.

“How long you have the virus, called viral shedding, depends on many factors including  your age, whether you have an underlying condition and how severe your disease is.” 


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