Nina Panikssery

5.

Weak guess, daycare environments are more conducive to disease spread than schools for older kids and the number of possible illnesses is very high.

There isn't just a limited number of things you catch once.

I zeted about this.

There's an image here.

Description.

A number of people sent me this link, an alleged study from UCL showing that frequent infections in nursery help toddlers build up immune systems, authored, of course, by a group of parents who all send their kids to nursery, what the British call daycare.

The link I was sent was actually a UCL Press release summarizing a narrative review paper and not a study itself.

Narrative reviews are susceptible to selection bias because, unlike systematic reviews or meta-analyses, there's no pre-registered search protocol or Prisma-style methodology requiring them to account for all relevant evidence.

But I decided to look into the narrative review more to assess its validity fairly.

I got access to the full publication.

Unlike the press release, which ignores these considerations entirely, it does engage with severity and age-related vulnerability, conceding that younger toddlers and babies suffer more from the same illnesses.

A section on immunology provides a detailed account of why infants under two are more vulnerable.

Their immune systems are much less effective at fighting the same infections for a plethora of well-understood reasons.

The review also cites a large Danish registry study, Kampjørgensen et al., that reports a 69% higher incidence of hospitalisation for acute respiratory infections in under-1s in daycare.

However, these severity findings are integrated into the review's conclusions and framing in an incredibly biased way.

The introduction describes severe outcomes as occurring in rare cases, and the conclusions focus on normalising the burden and advocating for employer understanding.

After establishing the immunological basis for why the same infection is more dangerous in a 6-month-old than a 3-year-old, it doesn't then ask the hard follow-up question.

Given this, is the pattern of starting daycare at 6 to 12 months optimal from a child health perspective?

Instead, the review frames this timing as a societal given.