Antibody research indicates coronavirus may be far more widespread than known Of 3,300 people in California county up to 4% found to have been infected.

A critical question in the path towards the future is how many people actually have protective novel coronavirus antibodies and possible immunity? Two research teams in California -- backed by armies of dedicated volunteers -- set out to answer this very question and the first set of results are in.

The first large-scale community test of 3,300 people in Santa Clara County found that 2.5 to 4.2% of those tested were positive for antibodies -- a number suggesting a far higher past infection rate than the official count.

Based on the initial data, researchers estimate that the range of people who may have had the virus to be between 48,000 and 81,000 in the county of 2 million -- as opposed to the approximately 1,000 in the county's official tally at the time the samples were taken.

“Our findings suggest that there is somewhere between 50- and 80-fold more infections in our county than what’s known by the number of cases than are reported by our department of public health," Dr. Eran Bendavid, the associate professor of medicine at Stanford University who led the study, said in an interview with ABC News' Diane Sawyer.

For the project, from just a finger prick, a drop of blood was used to reveal whether volunteers recruited through targeted ads online had protective antibodies in their blood left behind after the coronavirus. Volunteers were tested at three drive-through sites in the county.

Dr. John Brownstein, an epidemiologist at Boston Children's Hospital and an ABC News contributor, cautioned that the results for the California county are not necessarily representative of the U.S. population and noted the use of online ads to find participants could skew the candidate pool. But, he said, the work is "adding to this confirmation of what we've expected, which is a much larger number of cases than we ever anticipated."

"There has been wide recognition that we were undercounting infections because of lack of testing or patients were asymptomatic," Brownstein said.

Antibody tests are often touted by public health experts as a tool to help determine when Americans can get back to normal life, because they can determine not just whether someone has recovered but whether a person has been exposed to the virus in the past.

And while there is no guarantee of total, long-term immunity even if a person has antibodies, doctors hope that those who do have them may have some degree of immunity protection. Experts hope that could be a tool to help determine who could potentially more safely re-enter the workforce -- and just as importantly -- when.

Bendavid said the research, which has not yet been peer-reviewed, suggests that the large majority of the county, around 95%, is still without antibodies and for getting people back to work “what that means for things like, are we going to wait for people to get infected or get antibodies in order for them to get back to work... knowing that well upwards of 90% of the population doesn't have antibodies is going to make that a very difficult choice."

The initial data is the first to provide greater clarity about where a community is in the pandemic. But Bendavid cautions that the work was more illuminating about what’s happening on the community level than it was for any one individual.

“We have good confidence that we’re getting reliable information on the population. And that can be done because we know what proportion of the people who are positive we’re missing using this test,” said Bendavid.

The results suggests more research and analysis is needed to know how many people who tested positive for antibodies never knew they had the virus because they had no symptoms.

Public health experts are calling for more antibody tests and, until the U.S. has more widespread testing and contact tracing, say they still believe social distancing is a cornerstone to controlling the pandemic.

Bendavid told Sawyer the most important thing a person who has tested positive for antibodies to do is to “keep following public health guidelines.”

Scientists in California are moving quickly and carefully to mobilize testing with similar community antibody research underway in Los Angeles by Dr. Neeraj Sood at the University of Southern California.

Sood told ABC News the information from these antibody studies will help “the nation figure out what’s happening with this epidemic."

What to know about coronavirus:

How it started and how to protect yourself: Coronavirus explained

What to do if you have symptoms: Coronavirus symptoms

Tracking the spread in the U.S. and worldwide: Coronavirus map