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According to a study, how quickly a person’s immune system responds after infection with the coronavirus plays a crucial role in determining the severity of the disease.
Cambridge researchers studied 207 people who tested positive for Covid-19 over a three-month period and found that those who had no symptoms or mild cases had a robust immune response soon after becoming infected.
But people with severe cases requiring hospitalization had an impaired immune response, which led to a delayed and weakened attempt to fight the virus.
This undercooked response to infection is characterized by inflammation of several organs, which occurs immediately after a person catches the coronavirus.
Scientists say that abnormalities in immune cells can be the cause of the slow response to viral infection as well as the body’s inflammatory response, and can contribute to serious illness and also to “long Covid”.
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How quickly a person’s immune system responds after coronavirus infection plays a crucial role in determining the severity of the disease, study finds (file)
Dr Paul Lyons, co-lead author of the Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID) study, said: “ Our evidence suggests that the journey to severe Covid-19 can be established immediately after infection, or at the latest when they start showing symptoms.
“ This finding could have major implications for how the disease should be managed, as it suggests that we need to start treatment to prevent the immune system from causing damage very early on, and possibly even preventively in groups with high risk screened and diagnosed. before symptoms develop.
There is no cure for Covid-19 but treatments have improved since it emerged in China at the end of 2019.
Researchers at the University of Cambridge recruited a range of people who tested positive for the virus to see how the immune system’s response affected a person’s prognosis.
These people ranged from asymptomatic healthcare workers to patients requiring ventilation.
In the study, which has not yet been peer reviewed but is available as a preprint on medRxiv, the team analyzed blood samples taken regularly for three months. .
They compared the samples to those taken from 45 healthy people.
Researchers found evidence of an early and robust adaptive immune response in infected people whose disease was asymptomatic or mildly symptomatic.
An adaptive immune response occurs when the immune system identifies an infection and then produces T cells, B cells, and antibodies specific to the virus to fight against it.
Cambridge researchers studied 207 people who tested positive for Covid-19 over a three-month period and found that those who had no symptoms or a mild case mounted a robust immune response right after becoming infected (file)
These people produced the immune components in greater numbers than patients with more severe Covid-19, and in the first week of infection.
After that, the numbers quickly returned to normal.
There was no evidence in these individuals of systemic inflammation that could lead to damage in multiple organs.
In patients who needed to be hospitalized, the early adaptive immune response was delayed and deep abnormalities in a number of subsets of white blood cells were present.
Researchers say this suggests that an abnormal inflammatory component of the immune response is present even at diagnosis in people who progress to severe disease.
UCL professor Derek Hill, who was not involved in the study, said: “ This article … finds that there are signatures in early blood tests that are associated with the subsequent course of the disease ranging from mild to severe disease. symptoms.
“ Also, there is a clue in blood tests regarding those who may have a long COVID.
“ These are interesting results, but it’s important to note that a much larger study would be needed to determine whether the ‘signatures’ of the blood tests that the authors identified are reliable predictors of disease progression. , and whether this information could be used to help make treatment decisions.
The team also found that key molecular signatures produced in response to inflammation were present in patients admitted to hospital.
They say these signatures could potentially be used to predict the severity of a patient’s illness, as well as to correlate with their risk of death associated with Covid-19.
The study also provides clues to underlying biological cases of long-lasting Covid – where patients report experiencing symptoms of the disease, including fatigue, for several months after infection, even though they no longer test positive for the virus.
The team found that deep alterations in many types of immune cells often persisted for weeks or even months after infection with SARS-CoV-2, and these problems resolved very differently depending on the type of immune cell. .
While some heal as the systemic inflammation itself resolves, others recover even in the face of persistent systemic inflammation.
However, some cell populations remain markedly abnormal, or show only limited recovery, even after systemic inflammation resolves and patients are discharged from hospital.
Dr Laura Bergamaschi, the study’s first author, said: ‘It is these populations of immune cells that still have abnormalities, even when everything else seems to have resolved, that could be important in a long COVID.
“For some types of cells, they may just be slow to regenerate, but for others, including some types of T and B cells, it seems like something continues to stimulate their activity.
“The more we understand, the better able we will be to treat patients whose lives continue to be marred by the aftermath of COVID-19.
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