Study finds Covid measures delayed the development of Japanese 5-year olds by 4.4 months

This week, JAMA Pediatrics published a study by Sato et al. titled “Association Between the COVID-19 Pandemic and Early Childhood Development”. So let’s see what they did, shall we?

In this cohort study conducted in all accredited nursery centers in a Japanese municipality, baseline surveys of children aged 1 and 3 years…were conducted between 2017 and 2019, and participants were followed up for 2 years. Children’s development was compared at age 3 or 5 years between cohorts that were exposed to the pandemic during the follow-up and a cohort that was not.

A longitudinal study of Covid measures with a control group! Oh, I bet the results are gonna be good!

During the follow-up, the cohorts that were exposed to the pandemic were 4.39 months behind in development at age 5 compared with the cohort that was not (coefficient, −4.39; 95% credible interval, −7.66 to −1.27).

Okay, so by “good”, I meant clearly and unequivocally significant. Obviously the results for 5-year olds are utterly depressing. 4.39 months is the overall developmental delay, but among the eight sub-domains, noticeably larger delays were found in expressive language (5.64 months), social relationship with adults (6.41 months), and discipline (5.69 months).

However, it’s not all bad news. The pandemic-exposed cohort of 3-year olds didn’t show any overall delay and actually scored higher on various sub-domains than the pandemic-unexposed cohort.

So what explains these contradictory results? Sato et al. offer their thoughts.

With age, developmental differences across children magnify, and communication with non–family members becomes pivotal in their development.^1,2,28 Reduced communication with peers and teachers may have particularly affected the cohorts that were exposed to the pandemic at age 5 years…The pandemic increased the amount of time parents stayed at home, so increased 1-to-1 interactions within the family may have offset the negative outcomes of the pandemic among the exposed cohorts at age 3 years.

That makes sense: spending more time at home with mum and dad and less time outside of the house with non-family will have different effects on kids aged 3 and 5.

So can we blame Japan’s mask mania in any way for the delays among 5-year olds? Well, the word “mask” doesn’t even appear in the paper. Here’s what lead author Koryu Sato has to say.

I agree that the study can’t clarify one way or the other. The government didn’t explicitly recommend masks for kids at nurseries and pre-schools until early 2022 to coincide with the roll-out for the 5-11 Covid vaccine, so mask rules for kids at nurseries and pre-schools were quite varied during the study period. But all staff would’ve been masked, and staff themselves have said they feel staff masking impedes children’s language development.

Interestingly, the pandemic-exposed cohort showed larger delays in receptive language, expressive language, and language concepts in 2021 than in 2020, which is certainly consistent with the claim that widespread masking stifles language development. In contrast, the results for non-language sub-domains are similar in both years. These results are buried deep in the supplementary material, natch.

Subgroup Analysis by Follow-up Timing for the Association Between the Pandemic and Child Development

So we can add delayed early childhood development to the long list of undesirable achievements of Japan’s politicians and experts. But there’s one more point worth noting. Despite this study being widely reported in Japanese media, no one seems to have asked the authors an obvious question: “If you’ve had data showing negative effects of Covid measures since 2020, why did you wait till now to publish it?” I’ll try to answer that for them.

If this research had been published earlier, “anti-maskers” and the like may have used it to call for an end to any form of Covid cosplay for children around the same time as the government was promoting the Covid jabs for kids. This would’ve greatly inconvenienced the government since the whole point of the Covid measures was to generate demand for the Covid shots. So Sato et al. could’ve rung the alarm about delayed development long before the Covid measures were lifted, but prioritising the well-being of Japanese children would’ve required some bravery from them. I guess I shouldn’t be too harsh on them though. After all, almost nobody in the Japanese education system prioritised the well-being of Japanese children, so why should people who don’t even work with kids be expected to?