Children who catch every bug at nursery get sick less often once they start school

University College London

Why does every parent of a nursery-age child feel like they are living in a permanent cycle of runny noses, fevers, and stomach bugs?

Because they probably are. A new review published in Clinical Microbiology Reviews puts numbers on what millions of parents experience: a typical one-year-old starting nursery will face roughly 12 to 15 respiratory infections, two bouts of gastrointestinal illness, and one or two rash-causing infections in the first year of attendance alone. But here is the part that may soften the blow: those children tend to get sick less often than their peers once they reach school age.

The review was written by five researchers who are also parents of young children - a detail that is not incidental. The authors, drawn from University College London (UCL), the University of Cambridge, Cornell University, and North Middlesex University Hospital, came together precisely because they wanted to understand what they were living through.

The boot camp hypothesis

"As parents, we were all struck by how often our collective nine children became ill after starting nursery," said Dr. Lucy van Dorp, an infectious disease genomics researcher at UCL's Genetics Institute. "So we came together to do the first review of how often a child starting nursery will get sick in their first year of attendance and what can be done about it."

The answer to how often is: a lot. The review synthesizes evidence across epidemiology, immunology, and vaccination studies to build a picture of what is actually happening biologically. Young children are not getting sick because nurseries are dirty. They are getting sick because their immune systems are immature.

Newborns carry some protection through maternal antibodies transferred before birth, but this passive immunity wanes during the first year of life. At precisely the point when many children enter group childcare, their adaptive immune systems - the branch that learns to recognize and remember specific pathogens - are still developing. The result is an immune system encountering dozens of common viruses for the first time, with limited ability to fight them off quickly.

"It's normal for children to get sick a lot because their immune systems have never seen these bugs before," said Dr. Leo Swadling of UCL's Institute of Infection, Immunity and Transplantation. "But then nursery serves as a 'boot camp' for their immune systems, building up resilience for the years ahead."

Sick now or sick later

So does early exposure to all these pathogens actually help? The evidence suggests yes, but with a timing trade-off rather than a net reduction in total illness.

The review found that children who attend nursery at a young age experience more infections between ages one and five compared to children who stay home. But once school begins, the pattern reverses. Children without prior group childcare experience catch more illnesses in their early school years, presumably because they are encountering the same common pathogens for the first time - just later.

The data suggest that early exposure in group childcare settings confers a degree of acquired immunity to common infections. Children who have already battled through dozens of colds and stomach viruses arrive at school with immune systems that recognize and respond to those pathogens more efficiently.

The finding does not mean nursery attendance creates a net health advantage over the full course of childhood. It means the burden of common infections is front-loaded rather than eliminated. But for parents who worry that their toddler's seemingly constant illness is abnormal or a sign of a problem with their nursery, the data are reassuring: this is biology, not bad childcare.

What actually helps

The review emphasizes that vaccination remains the single most effective intervention parents can use to protect their children from serious nursery-acquired infections. The authors specifically mention the new MMRV vaccine, which protects against measles, mumps, rubella, and chickenpox in a single shot.

"Vaccines are a key way to protect children from serious infections in childcare, so we encourage parents to keep their children up to date with all available vaccines," Swadling said.

The researchers also stress practical measures: keeping children home while they are unwell, and potentially for a day or two after recovery depending on the type of infection. "While infections during nursery are normal and common, it's important to do what we can to mitigate their spread," said Dr. Charlotte Houldcroft, a virologist at the University of Cambridge and the study's corresponding author.

The cost to working parents

The review does not shy away from the economic and practical burden. All those infections produce a substantial knock-on effect for working parents, who must take time off to care for sick children and often get sick themselves. The near-monthly pace of respiratory infections during the first year of nursery attendance means frequent disruptions to work schedules.

"Employers need to recognise that it's normal for parents of young children to regularly need to take time off work to care for their children, and will also be more prone to getting sick themselves - but this will improve as the child ages," van Dorp said.

The situation does improve with age. Older children in nursery are less likely to test positive for a virus at any given time and less likely to show symptoms when they do. The monthly infection cycle gradually stretches out as the child's adaptive immune system matures and accumulates pathogen-specific memory.

Gaps in the evidence

The review has limitations worth noting. Most of the studies synthesized come from high-income countries, and nursery environments, childcare ratios, and vaccination coverage vary significantly across different settings. The 12-to-15 respiratory infection estimate is an approximation drawn from multiple studies with different methodologies, not a single definitive trial. The review examines common infections - the kind that are unpleasant but self-limiting in healthy children. It does not address the experience of immunocompromised children or those with chronic health conditions, for whom the calculus around group childcare may be different.

The "boot camp" framing, while intuitively appealing, also simplifies a complex immunological picture. Not all infections contribute equally to long-term immune training, and the mechanisms by which early pathogen exposure shapes immune memory are still being worked out in detail.

But for parents watching their toddler cycle through illness after illness, the core message is straightforward: this is normal, it gets better, and vaccines are the best tool available to reduce the severity of what comes through the nursery door.