The Single Factor That Most Strongly Predicts Whether Kids Will Infect Family Members With Coronavirus

It isn’t age. It’s how long you wait to get tested.

F. Perry Wilson, MD MSCE

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Kids are getting COVID, and with the highly-infectious Delta variant still surging in the US, I have a lot of concern about outbreaks once all the children are back in school.

Of course, while some kids get very sick from COVID-19, most do not, thankfully. But kids tend to live with adults and so a key question is how often infected kids pass COVID-19 to other family members. And this week, appearing in JAMA Pediatrics, we get the most granular data yet answering that question.

The study comes out of Ontario — where a unified health system allowed researchers to track all known positive COVID cases on a household-by-household basis. The timeframe is important here — data ranged from June to December of 2020 — so we are pre-vaccine and pre-delta variant. The researchers found 6,280 pediatric index cases — that’s where the first case in the household occurred in someone 17 or younger. They then checked how many people in the household tested positive for COVID within the next 14 days.

Let me start with the topline results — 27% of households with a pediatric index case had at least one other household member become infected. In any house where transmission occurred, on average 2 additional family members were infected.

This is interesting — an attack rate that is a bit lower than might be expected given the lack of vaccines during the study period. But we also see that when anyone in the house got a secondary infection, often more than one person got a secondary infection, which supports the idea that some people are just more infectious than others.

And the researchers were able to quantify that. For example, kids age 0–3 were more likely to transmit to a household member than those aged 14–17. This could be…

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F. Perry Wilson, MD MSCE

Medicine, science, statistics. Associate Professor of Medicine and Public Health at Yale. New book “How Medicine Works and When it Doesn’t” available now.