The researchers reviewed blood donations in December and early January and found evidence of antibodies to the new coronavirus in at least 84 samples from nine states – which may indicate that these people were infected with the coronavirus.
Many people wonder if they may have a coronavirus at the beginning of a pandemic or even before people knew the virus was circulating.
It would be hard to know unless someone did a coronavirus test then – which obviously didn’t exist. The symptoms are similar to those of many other flu-like infections: cough, fever, body aches, and possibly a sore throat.
And without a sample taken at the time of infection or not long after, it’s impossible to know if a particular person was infected then, said Dr. Ian Lipkin, a specialist in infectious diseases at Columbia University.
Antibody tests may indicate a previous infection, but not when that infection occurred.
“You can’t tell the difference between those infected in December or March or April,” Lipkin told CNN.
The human immune response to a viral infection, such as Covid-19, changes over time. Several studies have shown that antibody responses intensify immediately after infection and then change over time. It is not yet known how long the human body will maintain its immune response to coronavirus infection.
“There are tests that indicate the last infection in the first weeks of infection, but you can’t really tell after that,” Lipkin said. The only exception would be if someone had previously done a blood test that showed a negative for the virus.
But the study shows that blood donation could be an important source of information about the start of the virus’s circulation, researchers at the CDC and the Red Cross said. “These results also highlight the value of blood donation as a source for conducting SARS-CoV-2 monitoring,” they wrote in their report Tuesday. SARS-CoV-2 is the scientific name for the coronavirus that causes Covid-19.
Blood donations stored since last year could be tested for antibodies, although the type of test may be important. Several other coronaviruses cause colds, and tests can misidentify infections associated with those viruses, researchers at the CDC and Red Cross have noted.
“We clearly want to know how long this virus has been circulating,” Lipkin added.
“People are trying to figure out when this first appeared outside China.”