Common Cold Gives Children Cross-Immunity Against COVID-19: Study

Children pictured in a classroom at Waterview Primary School in Auckland, New Zealand, on July 4, 2018. Phil Walter/Getty Images

Children’s exposure to the common cold can give them cross-immunity against the COVID-19 virus, a new study by European scientists suggests.

Since the pandemic, there have been many hypotheses to explain the well-documented phenomenon that young children are much less likely than adults to be harmed by COVID-19 infection. One of them proposes that the common cold, which most children get exposed to at least six times a year, generates memory T-cells that can cross-react and kill cells infected with COVID.

To test the hypothesis, an international team of scientists analyzed 48 blood samples collected before the pandemic from children between 2 and 6 years old. They also examined 65 samples from unvaccinated and COVID-negative adults, as well as 58 samples from people who had recently recovered from COVID.

The scientists focused on the memory T-cell response to OC43, one of the four coronaviruses that cause the seasonal common cold. They were able to confirm that memory T-cells previously activated by OC43 do cross-react against the coronavirus causing COVID.

Upon analyzing blood samples, the scientists found that many children at age 2 have highly functional memory T-cells that cross-recognize the COVID virus. The memory T-cell responses against COVID are apparently stronger in 6-year-olds than in 2-year-olds.

From age 6, however, the frequencies and functional capacity of this preexisting immunity started to wear off, with adults older than 60 experiencing significantly decreased magnitudes of COVID-reactive and OC43-specific T-cell responses.

The reason why this protection wanes as one ages, according to the scientists, might have to do with the fact that the vast majority of those memory T-cells are contained within a cluster of cells that produce cytokine, a protein that regulates the immune system. The cytokine-producing T-cell population was substantially diminished in people in their 60s.

“These reactions are especially strong early in life and grow much weaker as we get older,” Annika Karlsson, the study’s corresponding author and an immunologist at Karolinska Institutet in Sweden, said in a press release.

“Our findings show how the T-cell response develops and changes over time and can guide the future monitoring and development of vaccines,” she added.

The study was published on March 14 in PNAS, the flagship journal of the U.S. National Academy of Sciences. The team encompasses researchers from the Karolinska Institutet, the Universities of Bern in Switzerland and Oslo in Norway, and Linköping University in Sweden.

The researchers did note that their study lacked samples from children older than 6 and younger adults, which will be necessary for further investigation.

“Next, we'd like to do analogous studies of younger and older children, teenagers, and young adults to better track how the immune response to coronaviruses develops from childhood to adulthood,” said Marion Humbert, a postdoctoral researcher at Karolinska Institutet.