Blood Tests Show 2.2 Percent Of RIers Have Coronavirus Antibodies

PROVIDENCE, RI — Newly released data from the Rhode Island Department of Health shows that an estimated 2.2 percent of residents in the state have COVID-19 antibodies in their blood.

Last month, the department randomly selected 5,000 households in Rhode Island to receive both the nasal swab, or diagnostic test, and a serology test, which checks for the presence of antibodies. The test process was completely voluntary, and testing was conducted at certain Stop and Shop stores around the state.

Dr. Philip Chan, a consultant medical director with the Rhode Island Department of Health, said 10 to 15 percent of people selected responded, which was a good sample size and around what the department expected. All members of selected households were invited to get tested, and only asymptomatic people were included. In the state's three-pronged testing approach, this study fell under the third, or proactive surveillance, arm.

The data shows that approximately 2.2 percent of residents have antibodies for COVID-19. The number was calculated with a 99 percent confidence interval, meaning researchers are very confident in the results.

"That number is lower than what I expected, if you'd asked me a few months ago," Dr. Chan said, adding that while it is good to see such low numbers, it reinforces just how much of the population is still very susceptible to the coronavirus.

Broken down further, the test results once again show, like other measures, that there is a large racial disparity in the distribution of cases. The breakdown is listed below, along with the possible range based on the confidence interval.

• Overall: 2.2 percent (1.0-3.9 percent)
• Hispanic/Latino: 8 percent (3-15 percent)
• Black: 5 percent (0.3-18.9 percent)
• White: 0.9 percent (0.1-2.4 percent)

The clear disparities underscore the need to focus virus prevention efforts in densely-populated areas and communities of color, ensuring there is equity in health care. This message echoes that of Director Nicole Alexander-Scott, who has repeatedly said that zip codes shouldn't determine health.

One of the main questions of serology testing is whether antibodies offer any level of immunity, Dr. Chan said, which is still being studied. Because it only shows a moment of time, it would be helpful to repeat this type of testing again in the future to compare differences, he said.

The key takeaway from the data should be that Rhode Islanders must continue to be careful, Dr. Chan said, carefully following social distancing guidelines and wearing a mask or fabric face covering when out in public. It also shows that her immunity in no way applies to the pandemic, he said, because that approach only becomes effective when the vast majority has some form of immunity from a disease, with from prior exposure or a vaccine.

"We're nowhere near that ... I wouldn't count on herd immunity," he said.