The probable answer to this question lies in how our immunity changes and develops as we age. After birth, our immunity develops rapidly, receiving signals and triggers from infections, vaccinations and allergens from the environment we interact with or the food we eat. The mix of stimulants helps build our immunity as we grow, fighting off infections or ensuring they are only mild illnesses, for example, a child with hand foot and mouth disease, HFMD, or chickenpox.
It is common to describe disease severity as being worse at the ‘extremes of age’, meaning that symptoms and signs of an infectious disease are often worse in infants and the elderly. The concept of immune ageing or ‘immunosenescence’ is when our immunity ‘ages’ and is less responsive, which becomes clinically apparent in people aged 60 years and older.
However, a systematic analysis published in Nature shows that disease severity is high during infancy but becomes less severe during early childhood until a child is around 10 years of age. Disease severity then rises again through adolescence and into adulthood. This shows that our immunity to diseases is low after birth but rapidly strengthens in early childhood before slowly tapering through our lives. This new evidence could provide some clues as to why adults seem to suffer from infectious diseases more severely than children.
The human immunological response remains a complex mystery but with ongoing studies that look at how our bodies respond to pathogens and factors such as changes in lifestyle and environmental triggers, we are a step closer to understanding our bodies and hopefully with this knowledge, we are able to design better healthcare interventions like vaccines or medicines.
Dr Khoo Yoong Khean
Scientific Officer, Duke-NUS Centre for Outbreak Preparedness