The September Immunity Dip: Why Children Often Get Sick After Going Back to School

For many parents, September is a month of getting everyone organised again: finding the lost water bottle, remembering PE kits, resetting bedtime routines, and preparing for the inevitable bugs that seem to make their way home from the classroom. After the excitement of new teachers, new classrooms, and seeing friends again settles in, it can feel like the first cold of the school year arrives as quickly as the school timetable.

 

A runny nose, a cough, a sore throat, or a child who suddenly seems more tired than usual can become a familiar part of the back-to-school routine. If this sounds familiar, you're definitely not alone. Many families notice that their children seem to get ill shortly after returning to school, and there's a good reason behind this seasonal pattern.

 

Parents often refer to this as the September immunity dip. It's a useful, parent-friendly description rather than a formally recognised diagnosis or single biological condition: the autumn rise in respiratory illness reflects several overlapping factors, including increased social contact, circulation of respiratory viruses, more time spent indoors, and changes to children’s usual routines.

 

After weeks of summer holidays, children suddenly return to busy classrooms where they spend hours close together, share books and equipment, play in groups, and encounter a wider variety of everyday microorganisms. For most children, the illnesses that follow are mild and pass with time, rest, and plenty of fluids.

 

When the immune system encounters a pathogen, it can mount a response and may develop specific immune memory. However, children don't need to become ill for their immune systems to develop, and infection is not risk-free. The focus is not on trying to create a germ-free childhood, but on supporting the everyday habits that contribute to children’s health.

Why do children get sick when school starts?

The biggest reason children often get ill after returning to school is simple: more contact means more opportunities for viruses to spread. During the summer holidays, children usually have more flexibility. They may spend more time outside, have fewer structured activities, and interact with smaller groups of friends and family.

 

Once school starts, children are suddenly spending more time indoors, sitting close together in classrooms, sharing stationery and equipment, taking part in group activities, and meeting classmates who may have been exposed to different viruses at different times.

 

Research using electronic health records found that medically attended acute respiratory infections increased when schools were in session. Among children aged five to seventeen, the risk was particularly elevated during the second week of term and remained higher after more than two weeks of school attendance.

 

This isn't to say that schools are unhealthy environments. It simply reflects the fact that bringing large groups of children together creates more opportunities for respiratory viruses to circulate. 

The September asthma peak: why autumn can be harder for some children

While most children experience nothing more than the occasional cold, the return to school is particularly important for children with asthma. Researchers have identified a seasonal increase in asthma flare-ups during early autumn, often occurring a few weeks after children return to classrooms. This pattern is sometimes referred to as the September asthma peak or September asthma epidemic.

 

A Canadian study found that asthma hospitalisations among school-age children increased around two to three weeks after the return to school. Similar, although smaller and later, increases were also observed among younger children and adults, suggesting that respiratory viruses spreading among school-age children may also affect households and wider communities.

 

The exact timing and size of this seasonal increase will not necessarily be identical across every country or region, but the pattern has been well documented in research. Respiratory viruses, particularly rhinoviruses, are thought to play an important role.

 

Rhinoviruses are among the most common causes of the everyday cold and usually lead to symptoms such as sneezing, congestion, and coughing. However, in children with asthma or virus-sensitive airways, respiratory infections can trigger inflammation and make symptoms more difficult to control.

 

Studies investigating children experiencing asthma exacerbations during the September peak have found respiratory viruses, including rhinoviruses, frequently present during these episodes. In one study, respiratory viruses were detected in 62% of children experiencing asthma exacerbations requiring emergency treatment, compared with 41% of children with asthma who didn't require emergency care.

 

It's important to remember that this is not because a child has a “weak immune system”. Asthma is a condition involving airway inflammation and sensitivity, and appropriate asthma management remains the most important way to reduce risk.

 

Before the new term begins, parents may want to check that inhalers and spacers are available, medication is within date, and the school has the correct information about their child’s asthma action plan. If symptoms have been difficult to manage, speaking with a healthcare professional before the start of term can help make sure children have the support they need.

 

Helping children adjust to the return to school

Although we can't prevent every cough and cold from making its way home from school, there are a few simple things that can make the transition into autumn easier.

 

One of the biggest changes after the summer holidays is often sleep. Later bedtimes, relaxed mornings, and fewer routines are one of the joys of school breaks, but suddenly switching back to early mornings can leave children feeling tired while they adjust.

 

It's worth starting the adjustment before the first day of term rather than waiting until the night before. Try moving bedtime and wake-up time earlier gradually, keeping weekend timings reasonably consistent and beginning a predictable wind-down routine around 30 minutes before bed.

 

The NHS recommends gradually bringing bedtime forward by around 5-10 minutes at a time and avoiding phones, tablets and other screens during the 30-60 minutes before sleep. A calming routine, whether that includes a bath, brushing teeth, reading together or quiet music, can help children recognise that it is time to wind down.

 

Sleep supports children’s mood, concentration, energy and overall wellbeing, making it an important foundation for the school year.

 

Nutrition is another important piece of the puzzle. Growing bodies need a variety of nutrients, including vitamins, minerals, protein and healthy fats, to support normal immune function and overall development. A varied diet built around fruit and vegetables, whole grains, protein sources and healthy fats is a good place to start.

 

Of course, anyone who has packed a lunchbox or tried to encourage a tired child to eat vegetables knows that it is not always straightforward. Busy mornings, changing appetites and picky eating are all part of family life, which is why some parents choose to explore additional nutritional support alongside healthy everyday habits.

 

Teaching healthy hand hygiene habits

Children are naturally curious, which means they touch everything: classroom tables, playground equipment, books, toys and, inevitably… their faces.

 

Handwashing remains one of the simplest ways to reduce the spread of everyday infections, but knowing when to wash is only part of the picture. Teaching children how to wash their hands properly can help turn good hygiene into an everyday habit.

 

Encourage children to wash their hands before eating, after using the toilet, after coughing or sneezing, after blowing their nose and after outdoor play.

 

Teach them to wet their hands, apply soap and rub their palms, the backs of their hands, between their fingers, around their thumbs and under their nails for around 20 seconds before rinsing and drying thoroughly. The NHS suggests washing for roughly the time it takes to sing “Happy Birthday” twice.

 

Handwashing is only one part of reducing the spread of respiratory infections. Good ventilation, covering coughs and sneezes and spending time outdoors can also help reduce transmission. No single measure prevents every infection, but together these habits can make shared environments healthier.

What does the science say about lactoferrin?

One ingredient that has gained growing scientific interest is lactoferrin, a naturally occurring iron-binding protein found in human milk and other bodily fluids. It's been studied for its role in several aspects of the body’s natural defence systems, including antimicrobial activity, immune regulation and iron metabolism.

 

Evidence suggests that lactoferrin has a role in supporting aspects of immune function and host defence, with research in children exploring its potential benefits across areas including gastrointestinal health, respiratory infections and immune regulation. 

 

Lactoferrin has a well-established biological role and an increasingly interesting evidence base, but it should be considered as part of a wider approach to children’s health rather than a replacement for good nutrition, sleep, hygiene or appropriate medical care.

 

Meet IMMUNE: Leapfrog’s science-led support for the school year

This is where IMMUNE comes in. At Leapfrog Remedies, we chose lactoferrin as the hero ingredient in IMMUNE because of the compelling scientific research surrounding its role in the body’s natural defence systems.

 

IMMUNE combines high-purity lactoferrin with vitamin C and zinc, which contribute to the normal function of the immune system when consumed as part of the recommended daily intake. Formulated for children aged four and over, IMMUNE is an easy-to-take, delicious chewable tablet designed to fit naturally into everyday routines.

 

For us, IMMUNE is about complementing the foundations that matter: a varied diet, good sleep, regular movement, and healthy routines. It can be particularly convenient during busy periods such as the return to school, when keeping on top of all those routines can feel like a job in itself.

Your September preparation checklist

A little preparation before the school gates open can make the transition into the new term feel much more manageable. Here are our top 10 non-negotiables:

 

1. Reset bedtime gradually before term begins.
2. Check asthma medication, inhalers, and action plans where relevant. 
3. Encourage handwashing at key times.
4. Teach children to cover coughs and sneezes.
5. Support good ventilation where practical.
6. Make time for outdoor play.
7. Keep meals varied and encourage regular fluids. 
8. Keep children home when they are too unwell to attend school.
9. Support immune systems with IMMUNE.
10. Speak to a healthcare professional about persistent, severe, or worrying symptoms.

Reference list

 

Back to school sleep tips. (2021). [online] National Sleep Foundation. Available at: https://www.thensf.org/back-to-school-sleep-tips/ [Accessed 7 Aug. 2026].

 

Eggo, R.M., Scott, J.G., Galvani, A.P. and Meyers, L.A. (2016). Respiratory virus transmission dynamics determine timing of asthma exacerbation peaks: Evidence from a population-level model. Proceedings of the National Academy of Sciences, 113(8), pp.2194–2199. doi:10.1073/pnas.1518677113.

 

https://www.facebook.com/nhswebsite (2020). Sleep and young children. [online] nhs.uk. Available at: https://www.nhs.uk/baby/health/sleep-and-young-children/ [Accessed 7 Aug. 2026].

 

Johnston, N.W., Johnston, S.L., Duncan, J.M., Greene, J.M., Kebadze, T., Keith, P.K., Roy, M., Waserman, S. and Sears, M.R. (2005). The september epidemic of asthma exacerbations in children: A search for etiology. Journal of Allergy and Clinical Immunology, [online] 115(1), pp.132–138. doi:10.1016/j.jaci.2004.09.025.

 

Mayorga, V.S., Navarro, R., Roldan, V.D.T., Urtecho, M., Tipe, S., Calvert, B., Wright, L.A. and Ochoa, T.J. (2025). Efficacy of lactoferrin supplementation in pediatric infections: A systematic review and meta-analysis. Biochemistry and Cell Biology, 103, pp.1–23. doi:10.1139/bcb-2024-0181.

 

NHS (2023). How to wash your hands. [online] nhs.uk. NHS. Available at: https://www.nhs.uk/live-well/best-way-to-wash-your-hands/ [Accessed 7 Aug. 2026].

 

Ochoa, T.J., Pezo, A., Cruz, K., Chea-Woo, E. and Cleary, T.G. (2012). Clinical studies of lactoferrin in children¹this article is part of a special issue entitled lactoferrin and has undergone the journal’s usual peer review process. Biochemistry and Cell Biology, 90(3), pp.457–467. doi:10.1139/o11-087.

 

Pasinato, A., Fama, M., Tripepi, G., Egan, C.G. and Baraldi, E. (2024). Lactoferrin in the prevention of recurrent respiratory infections in preschool children: A prospective randomized study. Children, 11(2), p.249. doi:10.3390/children11020249.

 

Sears, M.R. and Johnston, N.W. (2007). Understanding the september asthma epidemic. Journal of Allergy and Clinical Immunology, 120(3), pp.526–529. doi:10.1016/j.jaci.2007.05.047.