Only 3.2 percent of Pennsylvania residents tested this spring had antibodies to the coronavirus, according to recently 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 findings also indicate that the total number of coronavirus infections is likely much greater than the number of reported cases. In Pennsylvania, there may be 6.8 times the known number. The most recent state 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 had no external symptoms. It is possible that someone with antibodies develops immunity to the disease.
That’s why places like Chester and Delaware counties launched widespread antibody tests for front-line workers, though 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 get sick again.
“You shouldn’t extrapolate these estimates to make assumptions about population immunity until more is known about the correlations,” the CDC report warned.
Still, the prevalence of antibodies in 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.
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The CDC released new antibody test data this week from 4.9 million patients in the Philadelphia metropolitan area, including Cumberland and Lancaster counties, through its website and the Journal of the American Medical Association. Blood samples were collected during routine exams, not necessarily from people who looked for tests to detect COVID-19 symptoms, this April.
In all seven counties, including several of those most affected 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 metropolitan area.
Nationwide, the study estimated that the total number of coronavirus infections could be two to 13 times the number officially reported based on the results of the antibody test. As of Wednesday, the country was approaching 3.9 million cases with more than 139,000 deaths.
Why does all this matter?
The CDC 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 measures to help prevent the spread of COVID-19, such as wearing face cloths when outside the home, staying 6 feet away from other people, washing their hold hands frequently and stay home when sick. “
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And the relatively low antibody positivity rate, combined with uncertainty about whether the antibodies confer immunity and for how long, means that wide swaths of the population are still susceptible to the disease.
“Most of us are likely to remain very vulnerable to this virus and we have a long way to go to control it,” said Jennifer Nuzzo, an epidemiologist at Johns Hopkins. The Washington Post. “This study should put to bed any further arguments that we should allow this virus to affect our communities to achieve herd immunity.”
Although diagnostic tests are widely available in Pennsylvania, despite growing concerns about wait times and accessibility, antibody tests are not yet widespread.
However, several labs and university research programs are offering them. Patients should consult their insurance company to determine if antibody testing is covered by their policy.
Wallace McKelvey can be contacted at [email protected]. Follow him on Twitter @wjmckelvey. Find PennLive on Facebook.
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