www.lesswrong.com/posts/byiLDrbj8MNzoHZkL/daycare-illnesses

The claim says colds and flu do not build immunity in general because they mutate every year. That is not what the underlying immunology literature says.

• Influenza: CDC states that antibodies produced after infection or vaccination can help protect against future infections, and that prior flu infections affect how the immune system responds later. CDC also explains that flu viruses change over time, which can let them evade existing immunity—that is, mutation can make prior immunity less effective, not nonexistent.
• Common colds / rhinoviruses: A peer-reviewed review in Human Vaccines & Immunotherapeutics says protective immunity to rhinoviruses is largely serotype specific, and that antibodies are known to protect against re-infection with the same serotype. The difficulty is the existence of roughly 160 antigenically distinct rhinovirus strains, not that rhinovirus infections fail to generate immunity at all.

So the accurate statement is closer to: these infections often generate partial or strain-specific immunity, but that immunity is limited by viral diversity and evolution. Saying they "don’t build immunity in general" is incorrect.

This claim says the UCL press release entirely ignores severity and age-related vulnerability. But the press release itself explicitly addresses both:

• It says newborns have protection from maternal antibodies that wanes in the first year, leaving "infants - especially those starting childcare - more vulnerable to infections."
• It also says the authors' children sometimes came home from nursery with a bug that left them "feeling pretty poorly - even occasionally needing hospital care."

Because the press release directly mentions both increased infant vulnerability and the possibility of severe outcomes requiring hospital care, it is inaccurate to say it ignores those considerations entirely.