The Pandemic Changed Who Brings Illnesses Into The House

It’s often said that kids are like walking petri dishes, frequently getting sick and spreading germs to caretakers, siblings and classmates. According to Kinsa’s data, that common adage checks out: children were the origin of about 80% of illness transmission within households with both adults and children prior to the COVID-19 pandemic. 

Kinsa users can enter demographic information like age and gender into their profiles, which is all de-identified. We then can identify when there are two or more individuals with a fever in one household within a 1-10 day period, and we use this as a proxy for household transmission. 

The patterns of the directionality of transmission - which age groups transmit disease to others - were fairly consistent prior to the pandemic: about 55% of the transmission within households with both adults and kids was child-to-child, 25% was child-to-adult, 15% was adult-to-child, and 5% was adult-to-adult.

Once the COVID-19 pandemic hit, there was a distinct shift in these trends. The amount of transmission originating in children drastically decreased, with the amount of transmission originating in adults increasing to about 40-50%. There are a few factors that may have contributed to this: with kids staying home from school, there were much fewer chances for them to catch illnesses outside the household to bring home to others. Additionally, while children can catch, spread and become very ill from COVID, they are less likely to present with a fever than adults, so it’s possible we were less able to pick up these cases. 

Since summer, this shift has started to reverse, returning toward baseline. This may be related to the increase in non-COVID respiratory pathogens circulating in kids, such as RSV, and may also be related to shifts in social distancing policies. 

As the school year progresses, we anticipate that transmission among children will continue to increase toward baseline levels. To help prevent illness in schools, we recommend that students and teachers wear masks in the classroom even if vaccinated, to wash hands or use sanitizer frequently, and to increase the amount of ventilation in classrooms if possible.