Dr. Sydney Sewall, right, instructs a volunteer while filling a syringe with the COVID-19 vaccine at the Augusta Armory, in this Tuesday, Dec. 21, 2021, file photo, in Augusta. Credit: Robert F. Bukaty / AP

Some 133,000 more Mainers may have contracted COVID-19 than the state’s official case count reflects, according to a new federal study that provides a greatly expanded picture of the number of people who may have been infected with the virus since it arrived nearly two years ago.

The U.S. Centers for Disease Control and Prevention surveyed blood samples taken through January in search of COVID-19 antibodies that would show people had been infected with the virus. It did not look at antibodies produced by vaccination.

The numbers indicate 309,000 Mainers, or 23 percent of the state’s population, had caught COVID-19 by the end of last month. It suggests Maine’s official count, about 176,000 at the time, missed about 43 percent of the estimated cases in the state, a figure that is largely in line with national estimates, according to the Washington Post.

The national data suggested about 43 percent of Americans had contracted COVID-19 and a majority of children. Some 37 million people had contracted the virus in December and January, as the omicron variant of COVID-19 was ascendant.

Health officials have long cautioned that their case counts — a metric that has been downgraded in measuring the virus’ daily spread during the hyper-contagious omicron variant surge — likely do not capture the total picture. The case counts do not include infected people who never were tested for the virus or used at-home tests whose results weren’t reported to state health officials. Case counts also tally individual infections, so they can include the same people multiple times if they’ve contracted the virus more than once.

Gibson Parrish, an epidemiologist formerly of the CDC, said the difference between Maine’s official case count and the number of residents likely to have been infected wouldn’t have been so great if the state had been able to stay on top of all the positive test results that came in during the omicron surge.

The state is still working through a positive test backlog that at its height reached 56,000 samples that needed to be added to the state’s daily case count. The reporting of those figures began in mid-February, causing daily case counts to spike and be skewed.

Nirav Shah, the director of the Maine Center for Disease Control and Prevention, said on Tuesday on “Maine Calling” that the state is still processing a few thousand of those cases.

But Parrish said a high number of asymptomatic cases were also likely the culprit.

The omicron variant was notable because of its high transmissibility and manifestation in mostly milder cases. He said those factors have made daily case counts less reliable and pointed to hospitalizations and wastewater testing — two metrics state officials have recently leaned on more — as better depictions of the current state of the pandemic in Maine.

“I wouldn’t be surprised if there were tens of thousands of cases for the state of Maine that just aren’t picked up,” he said.

Robert Long, a spokesperson for the Maine CDC, noted in spring 2020 that many medical providers also diagnosed people without tests. He noted Maine and other states have not done universal testing since the pandemic’s start and have anticipated the cases they report would not represent the full picture.

“This is not a surprise,” he said.