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Exposure to small children linked to lower risk of severe COVID-19

Kaiser Permanente analysis adds to evidence that previous “common cold” exposure could have immunity benefits


Adults with young children — and exposure to their colds — were less likely to have severe illness from COVID-19 than similar adults without children, a Kaiser Permanente study finds.

The research, published in the journal Proceedings of the National Academy of Sciences, suggests that previous exposure to a coronavirus (the family of viruses to which COVID-19 belongs and which account for nearly a quarter of common colds) could offer cross-reactive immunity and provide resistance to severe illness from COVID-19.

Matthew D. Solomon, MD, PhD

“Every parent knows that young children are vectors for cold viruses, and adults who are exposed to them at home or through their work report getting sick often,” said lead author Matthew Solomon, MD, PhD, an adjunct investigator with the Kaiser Permanente Division of Research and cardiologist with The Permanente Medical Group. “But exposed adults often report they don’t get as sick after a few years. One possible explanation is that constant exposure to colds helps people develop some immunity to these viruses.”

Given the similarity between the COVID-19 virus and many common colds, Solomon added, “We asked the question: Could having young children and getting their colds protect you from Covid?”

Previous studies on COVID-19 provided initial evidence that people with prior common cold exposure gain antibodies and immune cell responses that are helpful in resisting the virus and severe COVID-19 illness. The Kaiser Permanente investigators wanted to test this idea using real-world data, comparing adults who have young children to those without, while balancing other risk factors that could cause severe COVID-19 illness.

The study examined medical records for 3,126,427 adult members of Kaiser Permanente Northern California from 2 years before the pandemic through its first entire year. The researchers split adults into 4 groups, based on the age of any children in their household: adults with children 5 and under, adults with children 6-11, adults with children 12-18, and adults without children.

The investigators then selected adults from each group who were similar in age and other risk factors for severe COVID-19 disease. This propensity-matching design would lessen the possibility of a result being related to a health risk factor, rather than exposure to children.

We asked the question: Could having young children and getting their colds protect you from Covid?

–Matthew D. Solomon, MD, PhD


The results were striking: adults without children who contracted COVID-19 were 49% more likely to be hospitalized and 76% more likely to have an intensive care unit admission than adults with COVID-19 who had children aged 5 and under.

“This is not proof of a causal relationship between exposure to small children and potential cross-immunity, but it provides some epidemiologic evidence of a signal,” Solomon said. “Could having a young child in daycare, and all those runny noses, somehow have protected you from severe COVID-19 illness? It’s possible, and our findings suggest that may be the case.”

Additional research confirming the findings could be helpful in future infectious disease pandemics, he added. “You might think about who has built-up immunity when making tough decisions about who could go to a workplace setting. Tests could be developed to identify such pre-existing immunity,” Solomon said.

Vincent Liu, MD, MS

Comparisons among the other matched groups were less dramatic. Parents of older children (aged 6-11) and parents of teens were both 9% more likely to have a COVID-19 infection, when compared with parents of young children, but these groups had similar rates of hospitalization and need for intensive care.

The study did not identify any potential protective effect from exposure to young children for having a COVID-19 infection. “This is a complex set of findings to interpret which benefits from Kaiser Permanente’s rich electronic health record data,” said senior author Vincent Liu, MD, MSc, a research scientist with the Division of Research. “Because this type of study can’t be done in a randomized fashion, we use these population data to search for signals that can inform our approaches to mitigating COVID-19. More research is needed and this study provides an intriguing place to start.”

The study was funded by The Permanente Medical Group’s Delivery Science and Applied Research Program.

Co-authors were Gabriel Escobar, MD, Yun Lu, MPH, David Schlessinger, MS, and Catherine Lee, PhD, of the Division of Research; Jonathan Steinman, MD, PhD, of Columbia University; and Lawrence Steinman, MD, of Stanford University.

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About the Kaiser Permanente Division of Research

The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 450 epidemiological and health services research projects. For more information, visit or follow us @KPDOR.

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