According to researchers from the London School of Hygiene & Tropical Medicine, young adults are more likely to experience severe symptoms from infectious diseases than children.
“We know infants are particularly vulnerable to infectious diseases due to their immature immune systems, and the elderly are vulnerable due to immune deterioration. Surprisingly, little is known about how the response to infection changes between these age extremes,” said researcher Judith Glynn.
Analyzing immune response
To understand how the body’s response to infections changes over time, the researchers analyzed information on over 30 different infections that spanned the era before vaccines and antibiotics through the present day. The severity of an infection was determined based on how many cases required hospitalization, how many cases ended in fatalities, and overall intensity of symptoms.
The researchers learned that a trend emerged in terms of when the severity of infections peaks and dips. While infants are highly susceptible to a number of infections, illnesses tend to be less severe by the time they reach school age; however, that intensity spikes again around the age of 20 and peaks again in older age.
This pattern was consistent for several infections that the researchers analyzed. Young adults experienced worse cases of chickenpox, tuberculosis, mononucleosis, and measles, among several other conditions. Infections like scarlet fever and Ebola were found to become more intense beyond the 20-year-old mark, while hepatitis and COVID-19 were found to increase with severity as consumers aged beyond 40.
The researchers plan to do more work in this area to better understand why these associations exist, as it remains unclear why young adulthood is linked with such a high vulnerability to infectious diseases.
“Extraordinarily, information on responses to infections by age has never previously been brought together for a wide range of infections, and the reasons for variation in severity outside the extremes of age have hardly been explored,” said Glynn. “Our results suggest peak immune response is reached during school-age, and then starts to drop off much earlier than currently thought, from as early as 15 years old in some cases. We also see age patterns in the immune response to some vaccines, in how the body handles some persistent viral infections, and in immune markers, that together support our interpretation.”