Why do some people experience symptoms for months after an infection?
After an infection, multiple biological processes can continue to smoulder simultaneously, but which mechanism plays the leading role in any given individual cannot yet be predicted or specifically treated.
Prolonged symptoms after an infection have been recognised for some time, but the cause differs by infection and by individual. After COVID-19, the biological changes have been studied most extensively. In people with long COVID, measurably different proportions of immune cells have been found, stronger antibody responses against both SARS-CoV-2 and the Epstein-Barr virus, and strikingly low levels of cortisol, the hormone that, among other things, dampens inflammation. These are genuine biological abnormalities, not merely subjective complaints.
Several mechanisms are likely at work simultaneously. Think of viral remnants persisting somewhere in the body, dormant viruses reactivating, microscopic blood clots in small blood vessels, a disrupted gut microbiome, and disturbances in the nervous system. Which mechanism plays the leading role in which patient is not yet clear. Patients with long COVID and people with ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome, a serious chronic fatigue disease) show strikingly similar abnormalities: in nearly nine out of ten, blood flow to the brain is too low when standing upright, and damage to small nerve fibres in the skin has been established in both groups. This suggests that both conditions follow a shared biological pathway.
Prolonged symptoms after an infection are not exclusive to COVID-19. After Giardia (an intestinal parasite), Lyme disease, sepsis, and other serious infections, a comparable pattern of fatigue, brain fog, and joint pain can develop. In Lyme disease, genetic predisposition also plays a role: people with a particular hereditary variant in an immune-sensor gene react excessively and retain joint inflammation even after the bacterium has disappeared. After serious infections, lasting changes in immune function can also remain: resistance stays suppressed for an extended period, which explains a greater susceptibility to subsequent infections. This has been established in cell and animal research; large clinical studies in humans are not yet available.
Women are at greater risk of post-infectious symptoms than men. Psychological trauma following a serious illness can worsen or perpetuate symptoms, although that is not a complete explanation. There is as yet no treatment that addresses the underlying problem; most insights come from observational research and the precise mechanisms are still under investigation.
Based on reviews and observational studies. No randomised trials or meta-analyses are available in this source set. Causality has not yet been proven for most mechanisms.
Why do older adults become seriously ill from an infection more quickly?
Ageing weakens the immune system in several ways simultaneously, making infections more dangerous. Keep vaccinations up to date and discuss nutritional deficiencies with your doctor, as these additionally increase vulnerability.
Can too little sleep make you more susceptible to infections?
Too little sleep demonstrably makes your immune system more vulnerable, including to infections and vaccinations. Make sure you get sufficient sleep, even though the exact numbers and thresholds are not yet precisely known.
What does chronic sleep deprivation do to your inflammation in the long run?
Chronic sleep deprivation demonstrably raises inflammatory markers in your blood and is linked to diseases such as cardiovascular disease and dementia; getting enough sleep is therefore one of the most concrete things you can do yourself to limit chronic inflammation.
Can a past coronavirus infection weaken your immune system for a long time?
A past coronavirus infection can temporarily disrupt the immune system, and in Long COVID possibly for an extended period. If you have persistent symptoms following your infection, it is worthwhile discussing this with your doctor, including with a view to rehabilitation.
Why do you get sick more often when you are on a diet?
A low-calorie diet can weaken your immune system through deficiencies in minerals such as magnesium, disrupted gut bacteria and suppressed immune responses. When dieting, pay attention to adequate micronutrient intake to limit this risk.
What are the symptoms of a weakened immune system?
The clearest signs of a weakened immune system are recurrent or unusually severe infections, but skin problems, autoimmune complaints, and an increased cancer risk can also be part of the picture. If you recognise this pattern in yourself or your child, discuss it with your doctor.