Millions of COVID-19 cases went undiagnosed during the first months of the pandemic, a new study suggests.
Researchers at the National Institutes of Health (NIH) analyzed blood samples from people across the country who hadn't received a Covid diagnosis.
They estimated that almost 17 million cases were missed nationwide and that for every COVID-19 case detected in spring and summer 2020, there were 4.8 undiagnosed infections.
Younger Americans, people of color, and those in the Northeast and Mid-Atlantic regions were all more likely to have Covid antibodies - lining up with known patterns of the virus in the U.S. during the first half of last year.
The teams says the findings provide new insight into just how often COVID-19 cases may go undetected because many patients experience few or no symptoms.
Researchers at the NIH estimate that 17 million Americans caught Covid in the early months of the pandemic. Pictured: A Detroit resident gets vaccinated in June 2021
Antibody test results show that, during the first half of 2020, about 8.6 percent of Americans in the Mid-Atlantic region and 7.5 percent of those in the Northeast got Covid
Since March 2020, more than 33 million Americans have been infected with the novel coronavirus and more than 600,000 have died.
But these numbers may be significant undercounts because millions of Americans likely got infected but were never diagnosed.
In the early months of the pandemic, many Americans suspected they might have Covid but were unable to get tested.
With limited numbers of tests available, many healthcare providers only tested people with specific, flu-like symptoms or travel history to China.
As the virus spread, however, scientists learned more about other symptoms - loss of smell, fatigue, muscle aches - that didn't fit their past testing criteria.
The U.S. also learned that many people who are infected with the coronavirus never show symptoms at all.
The combination of inaccessible tests and no-symptom cases led to many cases going undetected, especially during the early months of the pandemic.
For the NIH study, published on Tuesday in Science Translational Medicine, researchers selected study participants from a pool of 240,000 volunteers, ensuring the study group was representative of the overall U.S. population.
About 8,000 participants had their blood drawn between May and July 2020 and completed surveys, telling the researchers about their demographics and work experiences during the pandemic.
The team then tested the blood samples for antibodies, immune system proteins that indicate a patient's body has fought off a coronavirus infection.
Out of the 8,000 volunteers tested, 304 had Covid antibodies.
None of the volunteers were diagnosed for COVID-19 before taking part in
