Washington, Apr 11 (IANS): A new study has begun recruiting at the US National Institutes of Health (NIH) to determine how many adults in the United States without a confirmed history of COVID-19 infection, have antibodies to the virus, according to a release of the NIH.

The presence of antibodies in the blood indicates a prior infection. In this "serosurvey," researchers will collect and analyze blood samples from as many as 10,000 volunteers to provide critical data for epidemiological models, said the NIH on Friday, Xinhua news agency reported.

The results will help illuminate the extent to which the novel coronavirus has spread undetected in the United States and provide insights into which communities and populations are most affected.

"This study will give us a clearer picture of the true magnitude of the COVID-19 pandemic in the United States by telling us how many people in different communities have been infected without knowing it, because they had a very mild, undocumented illness or did not access testing while they were sick," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID).

"These crucial data will help us measure the impact of our public health efforts now and guide our COVID-19 response moving forward," he said.

Investigators will test participants' blood samples for the presence of SARS-CoV-2 antibodies, proteins the immune system produces to fight a specific infectious agent. A positive test result indicates previous infection.

To date, reporting of US cases of COVID-19 has mostly relied on molecular tests that determine the presence of the virus in a person's airways using a noninvasive cotton swab.

While these cotton swab-based tests rapidly and effectively identify active infection, they do not determine whether a person was previously infected with SARS-CoV-2 and recovered, according to the NIH.

"An antibody test is looking back into the immune system's history with a rearview mirror," said Matthew Memoli, principal investigator of the study and director of NIAID's Laboratory of Infectious Diseases Clinical Studies Unit.

"By analyzing an individual's blood, we can determine if that person has encountered SARS-CoV-2 previously," he said.

Investigators will analyze blood samples for two types of antibodies, anti-SARS-CoV-2 S protein IgG and IgM, using an enzyme-linked immunosorbent assay.

In blood samples found to contain antibodies against SARS-CoV-2, researchers may perform additional tests to evaluate the volunteers' immune responses to the virus. These data may provide insight as to why these cases were less severe than those that lead to hospitalization, said the NIH.