On Monday, Houston Mayor Sylvester Turner announced that the true number of local residents who had gotten the coronavirus as of September was four times the amount previously confirmed by positive test results, according to a blood sample study from the Houston Health Department.

The health department’s analysis found that at least 13.5 percent of Houstonians have contracted COVID-19.

“The virus was probably prevalent in our community [at] four times the reported numbers that we had,” Turner said, “which also underscores the importance of wearing these masks and social distancing.”

The eye-popping statistic was uncovered after the health department, in partnership with Rice University and Baylor College of Medicine, analyzed the level of COVID-19 antibodies found in blood samples given by Houston residents from a random sample of 420 local households. Between September 9-18, the health department collected blood samples from 678 willing locals.

“Our results show that an estimated 13.5 percent of Houstonians, which is approximately 250,000 people, had been infected with COVID-19 by September,” said Dr. Loren Hopkins, HHD’s chief environmental science officer.

The human body produces antibodies when a person is infected with the coronavirus, even if that person never shows any symptoms, so detecting antibodies in someone’s blood means that person had COVID-19 in the past, Hopkins explained.

She also revealed that the city’s antibody survey found that more women than men in Houston tested positive for COVID-19 antibodies. Black and Hispanic Houstonians were more likely to have antibodies than non-Hispanic white residents as well, and more residents under 40 had antibodies than people over 40.

A second round of the antibody study will be conducted in January, Hopkins said. In that next phase, 420 new households will be randomly selected to participate. All of the original participants from phase one will have their blood drawn and analyzed again as well, to measure any difference in the level of antibodies they have which will help figure out how long people can remain immune to the coronavirus after being infected.

HHD reported an additional 745 new cases of COVID-19 within Houston on Monday and six new local deaths from the disease, putting the city’s cumulative test-confirmed case total at 104,962 and Houston’s total death count at 1,493. Turner also announced that the city’s test positivity rate has reached 10.5 percent, marking three straight weeks of growth in the wrong direction and the highest rate in Houston since early September.

Turner touted the news that Houston’s own MD Anderson Cancer Center was one of four Texan hospitals that received the first shipments of Pfizer’s COVID-19 vaccine on Monday, which was found to be 95 percent effective and was approved by the U.S. Food and Drug Administration on Friday.

“Tomorrow, more of the vaccine will arrive in Houston” at Texas Children’s Hospital’s main hospital and at LBJ Hospital, St. Luke’s, Memorial Hermann and Houston Methodist, Turner said, although he reminded Houstonians that supplies will be extremely limited and reserved for frontline workers and nursing home residents initially.

“We know that frontline healthcare workers and residents of long-term care facilities are the first groups to be vaccinated,” Turner said, referencing the state health department’s guidelines for vaccine distribution.

“It will likely be months before anyone who wants it can get it, but the process is starting,” Turner said.

HHD Director Dr. Stephen Williams said that over 500 healthcare providers in Houston — from doctors offices to neighborhood drug stores — “have either signed up or are in the process of signing up” to provide the coronavirus vaccine once readily available.

In reference to a recent report from the White House coronavirus task force that said Texas as a whole needs to do more to slow down the virus’s spread amid a statewide surge in coronavirus cases and hospitalizations, Turner said he still isn’t convinced things are bad enough in Houston for him to order a local curfew, even though he promised he has the authority to do so and said he’s gone ahead and drafted up a potential curfew order, just in case.

“It is already prepared and ready to go if I decide to move in that direction, so we’ll just continue to look at the numbers,” Turner said.