Boston study: 90% of the population may not have been exposed to COVID-19 at all

BOSTON — Nearly 90% of the population of Boston has not been exposed to COVID-19 at all. That is if a Massachusetts General Hospital (MGH), and the Boston Public Health Commission (BPHC) study in four Boston neighborhoods holds true for the rest of the city.

The study evaluated community exposure to COVID-19 through a representative sampling of asymptomatic Boston residents. It found 9.9% of residents tested positive for antibodies and 2.6% are currently asymptomatic individuals testing positive for COVID-19.

In conclusion, approximately one in 10 residents in this study has developed antibodies and approximately one in 40 currently asymptomatic individuals are positive for COVID-19 and potentially infectious. Mayor Marty Walsh says it played a part in not reopening the city Monday May 18th.

“We can draw two preliminary conclusions from the results of this study,” said Walsh. "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. When May 18th comes, I can’t go to my mother’s house. After this study that shows me ninety percent of the people in Boston -- and that’s a conservative number -- so let’s say let’s be a little more liberal side and say it’s 80% of the people in Boston still have not come in contact with coronavirus. I’m not going to take that risk to my mother.”

More than 5,000 residents living in East Boston, Roslindale or within the boundaries of zip codes 02121 and 02125 in Dorchester were invited to voluntarily participate in the study, with total outreach representing more than 55% people of color. Approximately 1,000 residents expressed interest in participating and 786 residents were deemed eligible. Of those, 750 residents enrolled in the study and received the required testing.

Residents with symptoms or a previously positive COVID-19 test were disqualified from the study.

Baseline demographics of the 750 participants:

  • Median age is 42.4 years old
  • 61.6% are female, 38.3% male
  • 36.8% are from Roslindale, 25.1% are from East Boston, 23.2% are from 02125 in Dorchester and 14.9% are from 02121 in Dorchester
  • 62% are white, 18.7% are Black/African-American, 12% are Latinx/Hispanic, 2.3% are Asian/Pacific Islander and .13% are American Indian/Alaska Native. 1.6% preferred not to say and 1.6% are unknown. There were no significant differences in COVID-19 or antibody rates by race or ethnicity in this sample.

Prevalence of COVID-19 positivity in currently asymptomatic individuals ranged from 1.1% to 4.6%, while antibody positivity ranged from 6.3% to 13.3% by zip code.

  • East Boston: 1.1% tested positive for COVID-19, 13.3% tested positive for antibodies
  • Roslindale: 2.2% tested positive for COVID-19, 7.6% tested positive for antibodies
  • 02121 in Dorchester: 2.7% tested positive for COVID-19, 6.3% tested positive for antibodies
  • 02125 in Dorchester: 4.6% tested positive for COVID-19, 12.1% tested positive for antibodies

The city admits the 750 residents tested is a small sample size but did chose some of the neighborhoods most affected by COVID-19 while still maintaining a good ethnic balance. Though the study found no difference based on ethnicity, organizers acknowledge that is likely not the case in a larger sample sizes and that data will be crucial when deciding when and how to reopen the city.

“We have seen this disease impact certain populations disproportionately and so when we talk about opening up the city and making sure that people are staying healthy we want to make sure we do that equitably and that everyone has an opportunity to be healthy stay strong avoid the disease,” said Dr. Jennifer Lo, Medical Director Of The Boston Public Health Commission. “If we cherry pick in some ways, even if it is based on data, we put those people who are at risk of inequitable access to care even more so at risk.”

"Making sound decisions about safely reopening requires that we understand how extensively the virus has already spread in our community," said Peter L. Slavin, MD, president of Massachusetts General Hospital. "The testing that the teams from Boston and the MGH conducted shows that approximately 90 percent of the city's residents have not yet been exposed to the virus. We also know that COVID-19 will be with us for a while. It is vital therefore that we be thoughtful and careful about reopening, and that we continue to take actions - wearing masks, physical distancing, working from home when possible, limiting gatherings - that can prevent another surge of the disease."

Testing was conducted at three drive-through testing sites in East Boston, Roslindale and Dorchester.

Testing for COVID-19 virus is done by means of a swab of the nose and determines if you have the infection.

Antibody testing is done by means of blood drawn through a finger prick and detects whether your blood has antibodies that are present when the body is responding to an infection, like COVID-19.

Any resident who tested positive for the COVID-19 virus or the COVID-19 antibodies was provided with clear guidance and information on how to care for themselves and those around them.

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