Massachusetts General Hospital, which led the research in conjunction with the Boston Public Health Commission, launched the pilot study last month.
The goal was to test 1,000 asymptomatic city workers and residents to project likely infection rates in four Boston neighborhoods. Antibody tests and coronavirus tests were given to 750 volunteers in Boston who were not showing symptoms of the virus.
According to the results, 9.9 percent of participants tested positive for coronavirus antibodies. However, Dr. Afridi of MGH said it's unclear whether antibodies equals immunity to the virus.
"We are going to recommend people be very very cautious as they look at antibody results," said Dr. Afridi. "Specifically if they're positive for antibodies, we do not have data currently that says you're protected from reinfection."
Participants who said they thought they previously had COVID-19 were significantly more likely to test positive for antibodies. If the individuals had a fever in the last month, or a change in taste or smell in the last month, Dr. Afridi said they were also more likely to have antibodies.
While the study suggests around 90 people in Boston have not been exposed to the virus, it also found 2.6 percent of asymptomatic people tested positive for COVID-19. That means roughly 1 in 40 people may currently have the virus without showing any symptoms, and could still be infectious.
At the press conference announcing the study results on Friday, Health and Human Services Chief Marty Martinez said the rate of infections for people without symptoms was "concerning," and that the data is being used to help understand the spread of the virus in the city ahead of reopening.
"We know that some employers have looks at testing as a way to think about immunity moving forward as we think about reopening," said Martinez, "but as the doctor explained we do not have enough information to show you whether or not antibodies will protect you from future infection."
Mayor Walsh said the study shows that the social distancing measures are working, and he said the city's Public Health Emergency will remain in place. Walsh said he will also not be lifting the face mask guidelines anytime soon.
"The Public Health Emergency declared on March 15th in the city of Boston remains in place until further notice," said Walsh. "We will not be lifting it next week, or in the near future. The same applies for our guidelines for physical social distancing and face covering."
Walsh said he knows many people are feeling "worn down" after two months in isolation, but he said the city simply cannot afford any unnecessary setbacks which could lead to a second wave of COVID-19.
"What the study showed us in that 90 percent of Bostonians have not been impacted by COVID-19 as far as their physical health," said Walsh. "Think about all the procedures we've taken to get to this point... If we lax and take those safety nets away and we have a second surge... we'll be in a lot worse of a situation than we're in today."
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