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PLACER COUNTY, Calif. (KTXL) – Placer County teamed up with Stanford University’s School of Medicine to find out how many people had contracted COVID-19 despite public health efforts to slow infection rates.

Stanford researchers asked 20,000 people across the county to participate in an anti-body test, a little over 2,000 of them agreed.

“That 10%, we sent kits and they pricked their finger with a needle and dropped it onto a piece of filter paper and sent it back to us. And then we tested that for anti-bodies,” explained Dr. Julie Parsonnet, Professor of Medicine at Stanford.

Dr. Parsonnet said the results revealed a lot.

“What we found was only about 15% of the population had seen the SARS-CoV-2 virus up to March 2021. That most people, 85% of the people in Placer County we tested, had never been exposed to the virus and never mounted an antibody response,” she told FOX40.

The study also found that the actual number of COVID-19 infections in the county likely tripled the number of recorded cases, due in part to asymptomatic people not getting tested.

“We are unlikely to be able to control this infection by allowing it to just run through the population,” Dr. Parsonnet said.

Also noteworthy, those fully vaccinated had double the level of antibodies compared to those who caught the virus naturally, sending the signal to researchers that vaccines are key to protecting the population.

Data shows as of mid-April about one in four people living in Placer County are fully vaccinated, and if people continue to roll up their sleeves experts say we could be on a road to pre-pandemic life.

“If we can step to the plate in these next four-to-six weeks and get as many people as we can vaccinated, we’ll end up looking a lot more like Israel, where they’re now going out and enjoying life and not wearing masks and really getting back to normal,” Dr. Parsonnet explained.

On March 1, Placer County reported 19,861 COVID-19 cases.

That same month Stanford researchers identified 12.5% of people with COVID-19 antibodies. 

At that rate, researchers concluded the county of 400,000 people should have seen 62,139 cases for that month.