This week, Virginia began releasing information on how many people have been tested for coronavirus antibodies and how many of those tests have come back positive.
Antibodies are blood proteins produced by the immune system and can be an indicator of prior coronavirus exposure, not current infection. They may offer some level of protection from future infection, whether the individual ever developed COVID-19 symptoms or not.
Nearly half of the state's antibody tests have been in Northern Virginia. The Fairfax, Loudoun, Prince William and Arlington health districts have reported the most antibody testing in the state, with just over 15,000 tests combined. More than 1,000 people in those areas have already tested positive for coronavirus antibodies.
As antibody testing, also known as serology, becomes more widespread, public health officials may be able to use the results to determine how much of the population was exposed to COVID-19, even if a significant number of those individuals never developed symptoms.
"At the population level, using serology will help us get a better handle on what is that relationship between the cases we know about and that broader group of people who have mild or were infected, but no symptoms," said Dr. David Trump, a physician/epidemiologist who is studying antibody test results for Virginia's Office of Epidemiology.
The first two people to test positive for antibodies in Northern Virginia were in Arlington and Fairfax April 16.
Since then, more than 33,000 Virginians have been tested for antibodies, and 6.1% have come back positive.
The Northern Virginia rate is slightly higher at 7.1% positive. The Prince William health district has the highest rate in the area at 9.1% positive.
But Dr. Trump cautions against putting too much weight on those numbers.
"There's a whole mix of, you know, who's being tested and for what reason in that number," he said. "Also, it's a variety of tests that are being done."
The Food and Drug Administration has warned that some serology tests are deemed to be more accurate than others. So if you are planning to get tested, it's important to do your homework when choosing a lab and a test.
The I-Team has counted dozens of locations in D.C., Maryland and Virginia that are already doing antibody testing. They are required to report the outcome of those tests to public health officials.
Virginia initially came under fire for including serology tests along with its reporting of PCR tests, which detect active COVID-19 infections. Now the data is separated into PCR and non-PCR test numbers and results and each are updated in the online dashboard daily. A Virginia Department of Health spokesperson confirmed the "vast majority" of the non-PCR tests are serology, although a small number of antigen tests may be included as well.
The News4 I-Team began asking Maryland and DC officials for serology data on May 14, and neither has provided the number of tests conducted to date. Maryland would not even confirm whether it's tracking that information yet.