Study Shows Obesity Increases Risk For Contracting COVID-19—But Not Asthma

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Two and a half years into the COVID-19 pandemic, we’re learning so much about how this viral disease behaves. Henry Ford Health scientists were part of a recent National Institutes of Health (NIH) study that has uncovered details about how COVID-19 spreads among households with children, including who is most likely to contract COVID-19 and who is most likely to transmit the disease.  

“From May 2020 to February 2021, we monitored about 1,400 families across the country,” says Christine Johnson, Ph.D., M.P.H., a research scientist at Henry Ford Health. “We sent COVID-19 testing kits to each family every two weeks. We also used blood samples to measure COVID-19 antibodies and we took stool samples to look for the virus there. During that time frame, COVID-19 vaccines weren’t widely available. In some ways, what we found wasn’t surprising, but other findings were quite unexpected.”  

Here, Dr. Johnson shares eight interesting findings from the study.  

1. When kids contracted COVID-19, 75% of the time they had no symptoms. For teens, asymptomatic infection occurred 60% of the time and for adults, asymptomatic infection occurred 48% of the time. “This means they had the virus in their nose but didn’t know it, confirming that asymptomatic spread often occurs,” says Dr. Johnson. 

2. Kids had a lower viral load than teens and adults. When kids were carrying the virus, they didn’t have as much of the virus in their system as teens and adults—and their viral load didn’t correspond with the severity of their symptoms. “However, with adults and teenagers, the higher their viral load, the sicker they were,” says Dr. Johnson.  

3. Young kids were most likely to transmit COVID-19 in their household. Teenagers, on the other hand, were least likely to spread the disease. “You could jump to the conclusion that teens are more solitary, while young kids are usually huggers,” says Dr. Johnson. “I thought it was telling how frequently kids were asymptomatic yet were most likely to transmit the disease to someone else.” 

4. Having allergic asthma didn’t make someone more susceptible to contracting COVID-19. People who have allergic asthma (or asthma triggered by allergens like dust mites, pollen and pet dander) have fewer ACE2 receptors expressed in their lungs. (ACE2 receptors are what COVID-19 attaches itself to.) So, in theory, the fewer receptors you have, the less likely the virus is to take hold in your body.  

5. If someone had a food allergy, they were less likely to contract COVID-19. “No one has figured out why this might be,” says Dr. Johnson. “Younger people are more likely to have food allergies, but we adjusted for that. It’s a pretty striking find.”  

6. Obesity increased someone’s risk for contracting COVID-19. The study found that age didn’t matter: children, teenagers and adults who were obese were more likely to contract COVID-19 than those who weren’t. “If you are overweight, your immune system might not be in optimal condition to ward off the virus and you may have a higher viral load,” says Dr. Johnson. 

7. Minority families were at an increased for contracting COVID-19. The COVID-19 pandemic has stricken minority communities the hardest—and now this study has shown that they’re more likely to contract COVID-19, too. This could be due to a combination of factors, including more opportunity to be exposed, increased healthcare disparities and implicit bias, which is all the more reason to ensure equity in healthcare

8. School was the biggest public source of COVID-19 transmission. “Daycare wasn’t associated with COVID-19 infection, neither was going to a healthcare facility or the grocery store—just in-person school,” says Dr. Johnson. Help prevent the spread of COVID-19 by ensuring your children are vaccinated as they head back to school this fall

“This study was done before the COVID-19 vaccines, so it’s really informative to see how the disease spreads,” says Dr. Johnson. “58% of the time someone contracted COVID-19 in a household, someone else in that household contracted it. It would be interesting to see how vaccination would change the results of this study.” 


Henry Ford Health offers COVID-19 vaccines and boosters to established patients. Appointments can be scheduled in MyChart. For updates on booster guidelines and availability of vaccines by age group, visit henryford.com/coronavirus/vaccine-faqs.

Christine Johnson, Ph.D., M.P.H., is Chair of the Department of Public Health Sciences at Henry Ford Health. 

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