D.C. officials announced plans to conduct a citywide coronavirus antibody survey last month, but one week shy of the deadline, only about 10% of invited households have participated.

D.C. Health, in a partnership with the Centers for Disease Control and Prevention, randomly selected 839 households and invited them to complete a questionnaire and a blood test that would indicate whether someone has had and recovered from COVID-19, in order to learn more about the virus’s spread in the District.

“We had thought it would be easier,” says Dr. John Davies-Cole, D.C. state epidemiologist at the Center for Policy, Planning, and Evaluation, who is overseeing the survey. He notes that turnout has been good at the District’s mass testing sites. “[We thought] once people hear this, they will come and get tested, so it’s a little bit of a surprise.”

The city sent invitations out dated July 21, and the survey’s end date was originally August 15. As of August 7, only 56 households had done so, and the city needs a minimum of 560 households, or 10 people per census block to respond, in order to get “a full picture of what is going on in the District” based on its population, per Davies-Cole.

The city moved the end date to August 21 in hopes that more people will participate, but only 86 households had responded as of Friday.

Davies-Cole says that, because coronavirus can be transmitted through people who are asymptomatic and those who contract it may never even know, antibody testing can give the city a better sense of how the virus has spread among locals. Maryland and Virginia also announced plans for similar studies this week with the help of local hospitals.

Davies-Cole did not say which neighborhoods had the highest or lowest participation rates, noting instead that the overall number of participants is still so low that the city is focused on getting “responses from throughout the District.”

Some doctors have said antibodies might help protect people from catching the virus a second time, but health experts caution that immunity is not guaranteed just because someone tests positive.

D.C. began offering free antibody testing in June. The program was also supposed to end on August 15, but has been extended through next Friday at the city’s Hillcrest Recreation Center and Navy Yard sites.

Both sites will operate with extended hours: Hillcrest on Denver Street SE will be open from 10 a.m. until 8 p.m., and Navy Yard on L Street SE will be open from 9 a.m. to 7 p.m. As part of the survey, the city will provide free transportation to and from the sites, and participants will receive a $25 Visa gift card.

Residents can still get antibody testing through their doctors after that date, but it won’t necessarily be free. The federal CARES Act requires insurance companies to pay for the tests, but many labs do not accept insurance.

D.C. Health sent selected households a postcard reminding them about the survey in early August, and has been working to get the word out through community partners. It’s all part of an effort, Davies-Cole says, to encourage “folks who’ve been identified to participate to take advantage of it and help their communities.”