Antibody project serosurvey indicates 1 in 10 people in Maricopa County have had COVID-19

The results are in for a COVID-19 antibody study in Maricopa County that looked to find out how many people have been infected with the virus since the pandemic began.

The study found only a small percentage of people have been infected, underlying the importance of a vaccine and other protective measures, like mask wearing.

The study estimates 1 in 10 people in Maricopa County were infected, or about 470,000 people. That's far below the number needed to reach herd immunity, according to health experts.

It was an 11-day study conducted in mid-September by the Maricopa County Department of Public Health. 29 communities across the Valley were chosen at random, and samples were collected from 260 participants.

Coronavirus in Arizona: Latest case numbers

The findings show that about 10.7% of the Maricopa County population had tested positive for COVID, unbeknownst to some.

"That tells us what when a vaccine does become available, it gives us the number.. what we're already starting with and how many more individuals we need to receive herd immunity in Maricopa County," said Marcy Flanagan, Executive Director of Maricopa County Public Health.

That number, 50 to 80% in order to reach herd immunity and limit the spread of the virus.

MAP: Arizona Coronavirus cases by zip code

The serosurvey tells health officials that there is still a lot more of the population that is still at risk of getting infected.

For every case reported, there are about three to four cases that go unreported. They're either asymptomatic or have mild symptoms and didn't get tested.

"So if you're not feeling well, go and get tested. And if you find out that someone you were in contact with was positive, you should get tested and get your flu shot, especially if you're traveling," said Flanagan.

Going into the holiday season, and the surge we are seeing in the state, health officials are continuing to remind people to continue preventative measures, such as washing hands, wearing masks, and social distancing.

"This will be a hard one for the holiday season, which is really limit your gathering to less than 10 people and make sure you're doing it safely," added Flanagan.

For those celebrating Thanksgiving, lucky for us, we have great weather. Health officials are asking people to consider having their holiday dinners outside to help limit the spread.


In order to protect yourself from a possible infection, the CDC recommends: 

  • Avoid close contact with people who are sick.
  • Avoid touching your eyes, nose, and mouth.
  • Stay home when you are sick.
  • Cover your cough or sneeze with a tissue, then throw the tissue in the trash.
  • Clean and disinfect frequently touched objects and surfaces using a regular household cleaning spray or wipe.
  • Cover your mouth and nose with a cloth face cover when around others
  • Wash your hands often with soap and water for at least 20 seconds, especially after going to the bathroom; before eating; and after blowing your nose, coughing, or sneezing.
  • Monitor your health daily

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