The immune system is at its peak in school-age children and begins to decline far earlier than previously thought, according to new research.
A new study from the London School of Hygiene and Tropical Medicine suggested that ‘immune aging’ may start in the teens, with a rise in the severity of many infectious diseases apparent even by the age of 20. For illnesses including Covid-19, the rise in severity begins later, around the age of 40, the team found.
Professor Judith Glynn, lead author from the London School of Hygiene & Tropical Medicine, said: “We know infants are particularly vulnerable to infectious diseases due to their immature immune system, and the elderly are vulnerable due to immune deterioration. Surprisingly little is known about how the response to infection changes between these age extremes.”
In fact, the study – which included 142 datasets with information on patient age and disease severity for 32 different bacterial and viral infections, both before and after antibiotics and vaccines became widespread for certain conditions – is among the first to examine the changes in the immune system over a lifetime.
“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,” said Professor Glynn. “The finding that ‘immune aging’ could begin as early as young adults could be a catalyst for much needed new approaches to how drugs and vaccines are designed and scheduled.”
Speaking to The Telegraph, she added: “We hope this can give new clues into how to investigate infections, and how best to respond. What is it that children’s immune systems are good at doing, and adults are less good at?”
Severity was higher by the age of 20 years for polio, typhoid, tuberculosis, measles, smallpox, chickenpox, HIV, infectious mononucleosis and yellow fever, the study published in the journal Scientific Data showed.
Ebola, meningococcal meningitis, cholera, scarlet fever and lassa fever all showed increased severity from 20 onwards, while seasonal flu, brucellosis and hepatitis B were more severe from age 30 up.
For Sars, Mers, Covid-19 and hepatitis A, severity begins to increase from the age of 40.
The immune system is weak at birth, which is why newborn babies are known to be more susceptible to lots of infections. However, it strengthens rapidly as it is exposed to new bacteria and viruses. As people age, however, there is a reduction in the numbers of cells that can respond to new infections – called naive T-cells. This explains in part why the fatality rate for novel pathogens, like Covid-19, is so high among the elderly, who have less of these cells ready to fight them off.
The surprising thing in the new research is the suggestion that this aging of the immune system starts happening so early in life – although one theory is that at adolescence the body focuses its energy on growing and developing reproductive capabilities, perhaps at the expense of the immune system, which is functioning well enough by that point.
Prof Daniel Altmann, professor of immunology at Imperial College London, who was not involved in the study, said: “More than anything it emphasises how little we understand about the nuances of immune development across the life course and how this could play into a complex question such as susceptibility to symptomatic Covid-19.”
He added: “We shouldn’t forget that some of the highest antibody and T cell responses to the virus are seen in older people, yet this group tends to show poorer outcomes.”