Just 3.2 percent of Pennsylvanians tested this spring had coronavirus antibodies, according to newly released data from the Centers for Disease Control and Prevention, a sign that widespread immunity is unlikely and that many people are susceptible to the disease.
The CDC’s findings also indicate the total number of coronavirus infections is likely far greater than the number of reported cases. In Pennsylvania, there may be 6.8 times the known number. The most recent statewide total was 102,765, according to the state Department of Health .
Antibodies, produced as part of the body’s immune response, are a sign that a person already had COVID-19 even if they exhibited no outward symptoms. It’s possible someone with antibodies could develop immunity to the disease.
That’s why places like Chester and Delaware counties launched widespread antibody tests for frontline workers, although it’s unclear what immunity looks like or how long it lasts. And there have been documented cases of patients recovering from the disease only to fall ill again.
“Extrapolating these estimates to make assumptions about population immunity should not be done until more is known about the correlations,” the CDC report warned.
Still, the prevalence of antibodies across parts of the state is a useful data point as public health officials prepare for a likely resurgence of infection and a possible second wave in the fall.
READ MORE: Hospitals must continue to report coronavirus data to Pa. amid federal shakeup
The CDC released new antibody testing data this week from 4.9 million patients across the Philadelphia metro area, including Cumberland and Lancaster counties, through its website and the Journal of the American Medical Association. The blood samples were collected during routine screenings, not necessarily from people who sought out testing for COVID-19 symptoms, this April.
Across the seven counties, including several of the ones hardest hit by the first wave of infections, 3.2 percent of people tested positive for antibodies. For comparison, the same data showed positivity rates of 6.9 percent in the New York City metro area, 5.8 percent in Louisiana, 2.7 percent in Missouri, 1.9 percent in Florida and 1.1 percent in the Seattle metro area.
Nationwide, the study estimated that total number of coronavirus infections could be anywhere from two to 13 times the officially reported number based on the antibody test results. As of Wednesday, the country was approaching 3.9 million cases with mroe than 139,000 deaths.
Why does this all matter?
The CDC’s findings indicate that a significant number of people have been infected with COVID-19 without knowing it. Consequently, they may be spreading it to other, more vulnerable people.
As the report concludes: “The public should continue to take steps to help prevent the spread of COVID-19, such as wearing cloth face coverings when outside the home, remaining 6 feet apart from other people, washing hands frequently, and staying home when sick.”
READ MORE: Getting tested for coronavirus in Pa. is becoming more difficult amid wave of new infections
And the relatively low antibody positivity rate — compounded with the uncertainty around whether antibodies confer immunity and for how long — means wide swaths of the population are still susceptible to the disease.
“Most of us are likely still very vulnerable to this virus and we have a long way to go to control it,” Johns Hopkins epidemiologist Jennifer Nuzzo told The Washington Post. “This study should put to bed any further argument that we should allow this virus to rip through our communities in order to achieve herd immunity.”
While diagnostic tests are widely available in Pennsylvania, despite some rising concerns about wait times and accessibility, antibody testing is not yet widespread.
Several labs and university research programs are offering them, however. Patients should consult their insurance company to determine if antibody testing is covered under their policy.
Wallace McKelvey may be reached at wmckelvey@pennlive.com. Follow him on Twitter @wjmckelvey. Find PennLive on Facebook.
Read the ‘The hunt for Ray Gricar.’
Thanks for visiting PennLive. Quality local journalism has never been more important. We need your support. Not a subscriber yet? Please consider supporting our work.