Although vaccinations and boosters are the best way to prevent serious illness or death from COVID-19, a person can still contract the virus. However, it is likely to be less severe.

At the start of the pandemic, scientists scrambled to develop vaccines for COVID-19. These preparations are based on weakened whole viruses or pieces of the virus (antigens) that stimulate immunity and protect against infection. Experts developed several effective vaccines that have been instrumental in controlling the pandemic.

To receive full protection, a person requires initial vaccinations and follow-up booster shots. A full immunization course consists of three or four vaccinations depending on the individual and the specific vaccine. People may also need additional bivalent booster vaccines that protect against newer variants.

There are several reasons why a person may test positive after getting vaccinated. First, they may contract the virus. This is likely to be less severe and has fewer complications than if they were unvaccinated. Second, the test may report a false positive. It is important to note that the vaccine does not cause an infection.

This article looks at testing positive for COVID-19 after vaccination and what a positive test could mean.

A rapid lateral flow COVID-19 test.Share on Pinterest
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A person can contract the SARS-CoV-2 virus and test positive even if they are fully vaccinated.

Although COVID-19 vaccines are effective, they cannot prevent infection entirely. Instead, they limit the amount of virus in the body, meaning a person is less likely to become seriously ill.

After vaccination, the immune system creates antibodies against SARS-CoV-2, the virus that causes COVID-19. But, as with all vaccines, the antibody levels decrease over time. This waning protection, combined with the emergence of new variants, means a person has less protection.

How well a vaccine protects someone depends on their:

  • general health
  • age
  • sex
  • body weight
  • immune response
  • time since vaccination

Because vaccines cannot guarantee complete protection against COVID-19, people should still wear masks and adhere to social distancing and other guidelines. However, even when taking all reasonable precautions, a person can still contract the virus and test positive for COVID-19 after vaccination.

In addition, vaccines take time to stimulate immunity. They also may be less effective in people with compromised immune systems.

A person may also become test positive if they contract a new variant of SARS-CoV-2. The vaccine they received may not provide adequate protection against new variants. For this reason, it is important to stay up to date with boosters.

Rapid tests are point-of-care tests that can provide results in minutes. They are useful for home testing and quick results.

These tests work by detecting proteins (antigens) from the SARS-CoV-2 virus.

However, antigen tests are less accurate than molecular PCR tests, which detect genetic material from the virus. PCR tests do not provide instant results like rapid tests — instead, the sample must be sent to a lab for testing.

A false positive test occurs when the test incorrectly detects SARS-CoV-2 antigens in a sample from a person who does not have the virus.

There are several reasons why this might happen:

  • the test kit is outdated or damaged
  • reading the test before or after the specified time
  • cross-contamination
  • timing the test too early or too late in the infectious stage
  • quality issues in completing the test
  • presence of certain antibodies

No, the vaccine cannot cause a SARS-CoV-2 infection. None of the approved and authorized Covid-19 vaccines contain the live SARS-CoV-2 virus.

Instead, these vaccines work by training the immune system to detect and fight the virus.

Side effects that mimic COVID-19 symptoms are common. After a person gets the vaccine, they might experience chills, headache, and body aches. This is typical and a sign the person’s immune system is building protection against the virus — it does not mean the person has COVID-19.

A person should take a COVID-19 test if they have symptoms of the virus or were exposed to the virus.

If someone has symptoms, they should have a test immediately. Otherwise, they should wait five days after exposure. Testing too early can produce inaccurate results.

People who live or work in high risk settings, such as nursing homes or healthcare facilities, may require frequent testing as part of a regular screening program. This is to ensure the safety of employees and patients.

A person may also wish to consider testing before they have contact with someone at high risk for severe COVID-19. For example, if someone is planning to visit an elderly relative, it is a good idea to take a test beforehand. Vulnerable individuals include people over 60 with chronic health conditions or those that affect the immune system.​

COVID-19 vaccines are an effective way to test for an infection, but they are not perfect. Antibody levels from the vaccine can decline over time, and vaccines may not protect against new variants. This means that people should still take precautions even after being vaccinated.

A person may test positive for COVID-19 after vaccination because they have become infected with the virus or because of a false positive test result. False positives are more likely to occur with rapid antigen tests.

If someone has symptoms or was exposed to COVID-19, they should get tested.