A blood test to predict who is likely to have a severe response to Covid-19 could be available by autumn, allowing doctors to closely monitor those at the highest risk. 

There’s evidence that old age and the co-existence of other conditions such as heart disease, obesity, diabetes and immune defects are associated with a greater severity of the infection, the researchers said. But others require ICU treatment with no evidence of these factors. They wanted to find out why. 

The researchers, led by Dr Manel Esteller at the University of Barcelona, studied 400 people who had tested positive for Covid-19 who didn’t belong to any of the above risk groups. The study included people with asymptomatic infection or very mild symptoms, as well as those who had been admitted to hospital requiring respiratory treatment. 

The scientists were able to identify a common factor among the latter group. 

“We found that there were epigenetic variations – chemical switches that regulate DNA activity – in the individuals positive for the virus who developed severe Covid-19,” the researchers said.

“These modifications occurred mainly in genes associated with an excessive inflammatory response and in genes that reflect an overall worse state of health.”

The researchers noted that 13% of the world population are believed to have this epigenetic signature, and “this is the group at maximum risk that we must take special care of”. 

The idea is that a blood test – or maybe even a saliva sample, said the researchers – could recognise this signature, and “give the health professional a likelihood… of that person catching a high-risk Covid-19”. 

It could also be used to identify patients who should be given priority for receiving a vaccine or vaccine booster, according to researchers at the University of Barcelona. 

In separate research, scientists from the University of Manchester analysed the immune cell characteristics of more than 80 patients who’d been discharged from hospital following Covid-19 infection. The scientists wanted to monitor recovery and look for potential indicators of long Covid risk. 

They believe they may have identified an immune signature associated with poorer clinical outcomes, which could help identify those most at-risk from long Covid via a blood test in the future. However, they stressed more research is needed. 

“Follow-up studies will determine whether this signature can provide a tool to identify acute Covid-19 patients at risk of long Covid, enabling close monitoring and improved clinical management,” said study author Dr Madhvi Menon.