10% in the city have antibodies
Officials: Caution still needed moving forward
Nearly 10% of asymptomatic Bostonians have coronavirus antibodies, and more than 2% of that same apparently healthy group actually currently has the virus, according to the results of a sampling study done in several Boston neighborhoods.
“In conclusion, approximately 1 in 10 residents in this study have developed antibodies and approximately 1 in 40 currently asymptomatic individuals are positive for COVID-19 and potentially infectious,” the city said in a news release Friday morning.
The study, by Boston, Massachusetts General Hospital and the Boston Public Health Commission, involved what the city says is a representative sample of asymptomatic Bostonians, testing 750 residents and city employees over the past couple of weeks in East Boston, Roslindale and Dorchester for COVID-19 and the antibodies that suggest that a person already had it — and is now potentially immune to reinfection.
The exact figures are 9.9% of the subjects testing positive for antibodies, and 2.6% for currently having the virus — even though they had no apparent signs of the highly infectious disease.
Mayor Martin Walsh said the still-high number of people who haven’t been exposed to the virus — more people than the city expected, he said — means any reopening needs to be done very carefully.
“If 10% does represent the city antibody presence, that means 90% haven’t been exposed,” the mayor told reporters in a press conference.
If this sample is indeed representative of the city, it also means that between the known cases, there are many times more cases in the city of nearly 700,000 than the 11,527 confirmed positive cases in the city as of Friday.
MGH Dr. John Iafrate, one of the doctors who ran the study, said this means the city is nowhere near “herd immunity,” which he put at about 70% of people having been infected. He said that questionnaires of people who tested positive for antibodies showed that many reported having fevers or loss of smell or taste, common COVID-19 symptoms.
Iafrate stressed that there isn’t research yet that confirms that people with antibodies can’t get reinfected,
though doctors say they would be surprised if having antibodies didn’t confer some level of immunity.
This comes as the city and state tallies of deaths, cases and hospitalizations continue to improve after the peak in mid-to-late April, and officials chart out ways of beginning to reopen the economy. Gov. Charlie Baker’s stay-athome order will now end Tuesday, but the plan for what happens after that remains nebulous.
Asked if the city is planning any changes for next week as the governor’s order expires, Walsh said the city is taking it day by day.
“It’s a very fluid, changing situation,” Walsh said.
Several medical experts cautioned not to make too much out of the antibody test.
“I can’t get too excited about it,” said Dr. Robert Horsburgh, a Boston University professor of epidemiology. “If this is true, it confirms what we already knew — that there’s a lot of cases out there that we don’t know about. … The study is probably too small to get a real idea. I don’t think it changes a lot.”