More than 75% of Texans have COVID-19 antibodies, one of the world’s largest assessments finds

Vials of blood samples for serological testing. (Photo by UTHealth Houston)
The serological testing assessment relied on two types of antibody test to help identify what percentage of the Texas population has COVID-19 antibodies. (Photo by UTHealth Houston)

A year after launching one of the world’s largest COVID-19 antibody surveys, Texas CARES, public health experts at The University of Texas Health Science Center at Houston (UTHealth Houston) and the Texas Department of State Health Services (DSHS) are estimating that over 75% of Texans have COVID-19 antibodies.

Among their other key findings, the survey team determined that on average COVID-19 antibody levels peak about 120 days after infection and may return to undetectable levels as early as 275 to 500 days following infection. Additionally, people who are not vaccinated and were previously infected with COVID-19 have a lower number of antibodies compared with fully vaccinated survey participants.

“Texas CARES data revealed to us that fully vaccinated participants showed significantly higher antibody levels than those with a natural infection only,” said Eric Boerwinkle, PhD, dean, M. David Low Chair in Public Health, and Kozmetsky Family Chair in Human Genetics at UTHealth School of Public Health. “This suggests to us that vaccination may provide the highest level of protection, even for those who have had a prior COVID-19 infection and developed antibodies.”

The serological testing assessment, led by a team of public health experts at UTHealth School of Public Health and funded by DSHS, relied on two types of antibody test to help identify what percentage of the Texas population has antibodies in their blood, and likely some degree of protection from COVID-19. These results also helped determine prior infections in individuals who had few or no symptoms.

Participants were asked to complete a brief survey about their health and were then instructed to visit a participating clinic to have their blood drawn for three antibody tests administered several months apart. This allowed the survey team to measure antibody levels over a longer period of time and understand how long immune protection from natural infection and vaccination may last.

Texas CARES also had one of the largest samples in the nation of young people ages 5 to 19 years enrolled in a COVID-19 seroprevalence survey. The data revealed that more than 33% of the 3,889 Texas children who participated have antibodies to the virus, and of those, more than half (50.8%) were asymptomatic. Nearly half (44.9%) of parents reported the pandemic impacted their child’s mental health negatively.

“We are so thankful for all the Texans who volunteered to be in our survey,” said Jennifer Shuford, MD, MPH, Chief State Epidemiologist with DSHS. “We now have a better understanding of antibody levels in a diverse group of Texans with different experiences. Texas CARES participants are helping us understand the dynamics of the pandemic and what we can do to end it. And we’re not done yet.”

The survey team aims to continue to follow antibody levels over a longer period of time and will focus on enrolling more children in Texas CARES, particularly those from medically underserved communities.

With the recent U.S. Food and Drug Administration emergency use authorization granted for COVID-19 boosters, UTHealth and DSHS public health experts hope to better understand the effect of a booster vaccine on antibody levels.

Texas CARES is managed by a collaborative team from UTHealth Houston, consisting of public health experts across UTHealth School of Public Health’s six campuses in Houston, Dallas, Austin, San Antonio, Brownsville, and El Paso, and in partnership with DSHS, Clinical Pathology Laboratories, and The University of Texas System.

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