What age gets sick the least? A detailed look at immunity throughout life

September 28, 2025 •

4 min read

According to a systematic analysis of infectious disease outcomes, school-age children between 5 and 14 years old experience the lowest severity of illness. This raises the question of what age gets sick the least and how our immune system's resilience changes over the course of our lives.

Quick Summary

School-age children, typically between 5 and 14, generally get sick the least and experience the lowest severity of illness. This is due to a well-developed immune system combined with a history of exposure to pathogens, which builds a strong immune memory.

Key Points

Peak Immunity Age: School-age children, typically between 5 and 14 years old, experience the lowest severity of illness for most infectious diseases.
Why Children Get Sick Frequently: Infants and toddlers get sick often to build their immune memory through exposure to common pathogens, especially in group settings like daycare.
Immunity Decline: The immune system's function peaks around puberty and gradually declines thereafter in a process called immunosenescence, increasing vulnerability with age,.
The 'U-Shaped' Curve: Vulnerability to illness is highest at the two extremes of life—infancy and old age—and lowest in middle childhood.
Key Lifestyle Factors: Regardless of age, maintaining immune health depends on good nutrition, sufficient sleep, regular exercise, and stress management.
Older Adults' Vulnerability: As people age, a weakened immune system, slower response time, and chronic inflammation (inflammaging) lead to a higher risk of infection and severe disease,.

Understanding Immunity Throughout the Lifespan

From the moment we are born, our immune system begins a journey of development and adaptation. Our susceptibility to illness tends to follow a 'U-shaped' pattern, with high vulnerability in infancy and old age, and a period of peak resilience in between. Understanding this journey helps explain why different age groups experience sickness in different ways.

The Vulnerable Extremes: Infants and the Elderly

At both ends of the lifespan, the immune system is less effective, making these age groups particularly susceptible to infection and severe disease.

Why Infants Get Sick Often

Infants are born with immature immune systems that are still learning to recognize and combat pathogens. While newborns receive some protective antibodies from their mothers, this early protection wanes over time. Frequent exposure to new viruses and bacteria, especially in environments like daycares, is a necessary part of building a robust immune response, but it also means more frequent infections early on. The total number of illnesses may be similar for children in and out of daycare over the first few years, but those in daycare front-load their exposure.

Why the Elderly Face Higher Risks

With age, the immune system gradually declines in a process called immunosenescence. Key changes include:

Slower Response: A delayed reaction time to new or unknown pathogens.
Reduced Cell Production: The body produces fewer white blood cells and T-cells, which are critical for fighting infection.
Chronic Inflammation: A low-grade, persistent inflammation known as 'inflammaging' can increase vulnerability to illness and disease.
Lower Vaccine Efficacy: Vaccinations may not be as effective in older adults or provide protection for as long.

The Peak Resiliency of School-Aged Children

Research from the London School of Hygiene & Tropical Medicine highlights that school-age children (5-14 years) experience the lowest severity for most infectious diseases. By this age, several factors contribute to their heightened resilience:

Matured Immune System: The adaptive immune system is now well-developed. It has been exposed to numerous common pathogens, creating a strong bank of memory B and T cells.
Strong Immune Memory: This memory allows for a rapid and effective response to familiar infections, leading to milder symptoms and quicker recovery.
Improved Hygiene: Compared to toddlers, school-age children are typically better at practicing good hygiene, such as regular handwashing, which reduces the spread of germs.

The Gradual Decline Through Adulthood

Immune resilience begins to decline after puberty, often well before old age. This immunosenescence starts gradually, affecting young adults and continuing throughout middle age. The severity of many infectious diseases is higher in young adults than in school-age children, and this risk continues to increase with each decade. This is influenced by a combination of a slowly weakening immune system and lifestyle factors that accumulate over time.

How Immune Function Changes with Age

Thymic Atrophy: The thymus gland, which produces T-cells, shrinks significantly after puberty, reducing the production of new, naive T-cells.
Increased Chronic Conditions: The risk of developing chronic diseases like type 2 diabetes and heart disease, which can impair immune function, increases with age.
Inflammaging: Chronic, low-grade inflammation, or 'inflammaging', becomes more common and negatively impacts overall health and immunity.

Lifestyle Factors for a Strong Immune System

While age is a significant factor, a number of modifiable lifestyle choices can support immune health throughout life.

Healthy Diet: A balanced diet rich in fruits, vegetables, and other whole plant foods provides essential nutrients and antioxidants to support immune function. Conversely, malnutrition can impair the immune response.
Regular Exercise: Moderate, consistent physical activity can improve cardiovascular health, reduce inflammation, and enhance blood circulation, all of which contribute to a healthy immune system.
Adequate Sleep: Quality sleep is critical for immune function. Sleep deprivation can reduce the effectiveness of the immune system. Aim for 7 to 9 hours per night.
Stress Management: Chronic stress elevates the hormone cortisol, which can suppress the immune response over time. Finding effective ways to manage stress is crucial for immune health.
Vaccinations: Staying current with recommended vaccines helps prime the immune system to fight specific infections before they take hold.

For a deeper dive into improving immune function, exploring resources like the Harvard Health article on boosting immunity can provide additional strategies and insights.

Comparison of Immune Resilience by Age


Age Group	Typical Illness Frequency	Immune System Characteristics	Key Contributing Factors	Vulnerability
Infants (0-4)	High (6-12 illnesses/year)	Immature, still developing, relying initially on maternal antibodies.	Lack of prior exposure, immature immune system, frequent germ contact.	High
School-Age (5-14)	Lowest severity & frequency	Mature, with built-up immune memory from early childhood exposure.	Developed immune memory, improved hygiene habits, physical fitness.	Low
Young Adults (15-29)	Increases slightly from childhood	Gradual decline begins (immunosenescence starts); strong adaptive memory.	Beginning of immune decline, lifestyle factors, chronic stress.	Moderate
Older Adults (65+)	High frequency & severity	Significant decline in function, weaker response, chronic inflammation.	Immunosenescence, chronic conditions, lifestyle factors, reduced cellular repair.	High

Conclusion

While school-age children may enjoy a period of peak immunity where they get sick the least, health is not a fixed state. The immune system is a dynamic, evolving system that is constantly being influenced by age, lifestyle, and environmental factors. For everyone, regardless of age, focusing on a healthy, balanced diet, regular exercise, adequate sleep, and effective stress management remains the best defense against illness. Understanding these age-related patterns allows for a more proactive approach to health and wellness throughout one's entire lifespan.

Frequently Asked Questions

While it is complex and influenced by many factors, research suggests the human immune system is most resilient during the school-age years, specifically between 5 and 14, after it has been trained by early exposure but before the natural decline begins,.

Young children, particularly infants and toddlers, get sick frequently because their immune systems are still developing. Exposure to common viruses and bacteria is necessary for them to build a robust immune memory. This process, while leading to more frequent illness in early childhood, builds resilience for the school-age years,.

Yes, to an extent. Early exposure to pathogens helps train the immune system and build immune memory. Children who attend daycare, for instance, may get sick more often in the preschool years but less frequently during elementary school because they have already developed immunity to many common infections.

Immunosenescence is the age-related decline of the immune system. In older adults, it leads to a slower immune response, reduced effectiveness of vaccines, and increased susceptibility to infections, chronic diseases, and severe illness,.

Lifestyle choices are crucial at every age. Good nutrition, regular exercise, adequate sleep, and stress management can help support immune function and resilience, regardless of where a person is in the lifespan,.

The thymus gland is where T-cells mature. After puberty, the thymus begins to shrink, or involute, reducing the production of new T-cells. This is a significant contributor to the gradual weakening of the immune system with age,.

For most infectious diseases, severity is lowest in school-age children and rises thereafter. However, some infections, like dengue, can be most severe in school-aged children, while others, like diphtheria and E. coli, show slightly different patterns. The J-shaped curve (lowest severity in childhood, rising with age) is common for many diseases.