One in 10 Bostonians Has Been Exposed: About 90 percent of Bostonians have not been exposed to the new coronavirus that causes COVID-19, an antibody study conducted by the city and Massachusetts General Hospital found.

Mayor Martin Walsh and the hospital announced Friday that the study that tested 750 asymptomatic residents in East Boston, Roslindale and two Dorchester zip codes revealed that 9.9 percent tested positive for COVID-19 antibodies and 2.6 percent tested positive for active COVID-19.

Dorchester's 02121 zip code had a 2.7 percent positive rate for COVID-19 and 6.3 of participants tested positive for antibodies. Dorchester's 02125 zip code had 4.6 percent of participants test positive for COVID-19 and 12.1 percent test positive for antibodies.

The city said the results suggest 1 in 10 residents have developed antibodies and approximately 1 in 40 currently asymptomatic individuals are positive for COVID-19 and potentially infectious.

"We can draw two preliminary conclusions from the results of this study," Walsh said. "First, that the actions we took early on in this pandemic made a real difference in slowing the spread and, second, that the majority of our population still have not been exposed to the virus. This underscores what we already know, that we have to move cautiously and stay focused on what got us this far. This can be done by a gradual, phased-in approach to reopening that includes clear health criteria and safety guidelines for each industry and depends on testing and hospital metrics reaching certain benchmarks, and continuing to move in the right direction."

In East Boston, 1.1 percent of participants tested positive for COVID-19 and 13.3 percent tested positive for antibodies. In Roslindale, 2.2 percent tested positive for COVID-19 and 7.6 percent tested positive for antibodies.