For a couple of months, I’ve been calling for more antibody tests of representative samples to see how close we are to Herd Immunity. From the Boston Globe:
“This is a sample of residents in four zip codes,” Mayor Marty Walsh said of the coronavirus study results. “It does not give us a defined, citywide picture.”
By Christopher Gavin, Boston.com Staff
May 15, 2020 | 3:10 PM
Boston officials Friday released the results of the coronavirus and antibody testing performed on 750 asymptomatic residents in some of the city’s neighborhoods hardest hit by the ongoing pandemic.
The study, designed to help evaluate community exposure to the virus through representative sampling, found that of those tested in East Boston, Roslindale, and parts of Dorchester,
These are kind of dumpy and diverse neighborhoods.
9.9 percent tested positive for antibodies and 2.6 percent tested positive for the coronavirus, officials said.
Assuming no overlap, I come up with 9.9% previously infected plus 2.6% currently infected = 12.5% ever infected or 1 out of 8. But, the survey excluded people in the hospital or who had previously tested positive or who had died.
… Walsh, elaborating on the study’s results at a press conference Friday afternoon, said the antibody rate is “lower than what we would have expected from earlier models of the virus’s spread.” …
“I want to be clear that this is a sample of residents in four zip codes. It does not give us a defined, citywide picture,” Walsh said. “But the results do suggest some lessons about how we move forward.”
Over 5,000 residents in Roslindale, East Boston, and within the boundaries of the Dorchester zip codes 02121 and 02125 were invited to voluntarily participate in the study earlier this month. Roughly 1,000 people expressed interest, and 786 were determined to be eligible, according to officials.
Of those individuals, 750 people enrolled and received testing. Anyone with COVID-19 symptoms or who had previously tested positive were disqualified from participating.
Testing occurred over a two-week period at three drive-through sites. Coronavirus testing was conducted through nose swabs, while antibody testing was carried out through blood drawn from finger pricks.
People of color represented over 55 percent of the overall outreach, although the majority, or 62 percent, of those tested were white, 18.7 percent were Black/African American, 12 percent were Latinx/Hispanic, 2.3 percent were Asian/Pacific Islander, and 0.13 percent were American Indian/Alaska Native, data shows.
In the marketing research business, everybody knows that white women are the most cooperative group for participating.
“We ended up with a demographic cross section that was not a perfect match for our population, but it did draw significantly from each of our different neighborhoods and communities,” Walsh said.
Statistics released by the city have shown the coronavirus is impacting Black residents at a higher rate than white residents, although officials said the test results showed “there were no significant differences in COVID-19 or antibody rates by race or ethnicity in this sample.”
Antibody rates yielded from the study also showed no difference among the occupations of participants, from frontline, essential workers to the swaths of the workforce currently doing business from home, experts said.
As of May 7, 3,865 residents in Dorchester’s 02121 and 02125 zip codes had been tested since the onset of the pandemic, with 36.2 percent of them testing positive for the coronavirus.
Dorchester has a population of 88,000, so 1.6% of the population weren’t eligible because they were already positive.
Of 3,053 residents tested in East Boston, 38.7 percent had tested positive, and among 1,937 individuals tested in Roslindale, 29.9 percent had tested positive, city data shows.
Walsh said Friday varying numbers between neighborhoods are an “indication of how localized the spread can be and how targeted our response needs to be and needs to continue to be.”
Boston had logged 11,395 coronavirus cases as of Thursday and had a total of 4,089 recoveries so far, with a continuing decline in the number of active cases, according to the mayor. So far, 551 city residents have died due to COVID-19 complications.
The city of Boston’s population is 695,000. So if, say, 1/8th have been infected, that would be around a 0.63% Infection Fatality Rate.
… Dr. Anthony Iafrate, director of the Center for Integrated Diagnostics at MGH, said the study results capture just a snapshot of the virus spread at one moment of time, and pointed out that the antibody rate is by no means near the 70 percent threshold estimated by medical experts that’s needed for “herd immunity.”
“We’re not there,” he said. “We’re not at the 70 percent, ‘We’ve all had it, we’re safe and past this.’ We’re also not at 1 or 2 percent, which you might expect in a more rural community … where the risk of transmission might be low. So we’re somewhere in between an environment where the transmission is low and the risk is low and where we have herd immunity — and that’s a fairly anxious place to be.”
Median age: 42.4 years old
Sexes: 61.6 percent are female, 38.3 percent male
Neighborhoods: 36.8 percent are from Roslindale, 25.1 percent are from East Boston, 23.2 percent are from 02125 in Dorchester and 14.9 percent are from 02121 in Dorchester
Race: 62% are white, 18.7 percent are Black/African-American, 12 percent are Latinx/Hispanic, 2.3 percent are Asian/Pacific Islander and .13 percent are American Indian/Alaska Native. According to officials, 1.6 percent preferred not to say and 1.6 percent are unknown.
East Boston: 1.1 percent tested positive for COVID-19, 13.3 percent tested positive for antibodies
Roslindale: 2.2 percent tested positive for COVID-19, 7.6 percent tested positive for antibodies
02121 in Dorchester: 2.7 percent tested positive for COVID-19, 6.3 percent tested positive for antibodies
02125 in Dorchester: 4.6 percent tested positive for COVID-19, 12.1 percent tested positive for antibodies