Four Utah cities have begun administering antibody tests to residents who think they may have been exposed to or infected with COVID-19 but didn’t experience any symptoms.

This testing began last week in Bluffdale, Draper, Riverton and Vineyard.

The screening is aimed to detect antibodies present in Utah residents, which allow their immune systems to fight COVID-19. If the antibodies of a specific virus are present, that means they were exposed or infected with the virus. In the case of other sicknesses, individuals may have received a vaccination to prevent contracting it in the first place.

Antibodies are important to understanding the spread of COVID-19 across the country, determining if the country is close to reaching herd immunity: a collective resistance to the spread of the virus because of a high number of immune persons.

It’s also important to understand the true number of people who have been infected with the virus, the mayors of the four cities said in a joint statement. These tests give scientists an idea of how far the virus has spread since a number of those infected never showed symptoms. Testing has mainly been encouraged for those with symptoms relating to COVID-19.

“We believe a central component to beating COVID-19 is to test our residents,” the mayors’ statement said. “We need to know our true infection rate so we can take actions to limit spread, conduct contact tracing and make future data-driven public policy decisions. We invite all our residents to consider being tested for COVID-19 antibodies as we continue to battle this virus.”

Residents can make an appointment online and will be tested on a first-come-first-served basis. Antibody tests will cost $69.99 per person, which can be reimbursed by insurance payment plans. The tests are conducted through finger-prick blood sampling.