Just a small fraction of people tested for antibodies in the District have them.

According to a Washington Post investigation, out of more than 13,700 blood samples collected by the city’s public health lab in a month, fewer than 6% (or 809 people) carried antibodies.

The presence of antibodies can indicate if a patient had a past infection with the virus that causes COVID-19. Antibodies are proteins that help fight off infections and can provide protection against getting that disease again—that is, immunity.

While some doctors say the presence of antibodies might protect people from contracting the virus again, others, including the CDC health officials, are not sure a positive antibody test guarantees immunity against COVID-19. Scientists also aren’t sure whether a person needs a certain volume of antibodies to protect them against the virus, nor how long those antibodies remain effective in the body.

LaQuandra Nesbitt, the director of D.C.’s Department of Health, stressed that much is still unknown about the coronavirus. She has urged District residents to continue following social distancing guidance, wearing face masks and washing their hands, even if they tested positive for antibodies.

The city is selecting 850 random residents to take an antibody test in exchange for $25 compensation. District health officials hope this will reveal information from a diverse range of people that will help ongoing research efforts.

D.C. will continue to offer free antibody tests until August 15. Residents can get tested at Hillcrest Recreation Center and Navy Yard in southeast DC and Takoma Recreation Center in the northwest.

An antibody test may not show if you have a current COVID-19 infection because it can take up to three weeks after infection for your body to make antibodies. To see if you are currently infected, you need a viral test which uses samples from your respiratory system, such as a swab from the inside of your nose.