People who have fallen ill with flu can suffer long-term symptoms in a similar way to long Covid, a study suggests.
The Oxford University research analysed health records of people diagnosed with flu and Covid, mainly in the US.
The two groups – both with just over 100,000 patients – included people seeking healthcare for symptoms three to six months after infection.
These included problems such as anxiety, abnormal breathing, fatigue and headaches.
There were signs that Covid patients were more likely to have long-term symptoms – 42% had at least one symptom recorded compared with 30% in the flu group.
Both groups included people who were likely to have been quite ill with the viruses so the rates of persistent illness should not be seen as representative of the general population.
But the researchers said it did suggest both viruses could cause long-term problems that took time to get over.
Prof Paul Harrison, one of the lead researchers, said: „Many of us who have experienced flu know how you don’t always feel completely better as quickly as you’ve been hoping or expecting to.”
The higher rate in the Covid group could have been influenced by the fact that people may be more likely to seek care for long-term symptoms or the way symptoms are recorded for Covid.
However, on balance they said it was likely persistent symptoms were more common for Covid than flu.
The study, published in the journal PLOS Medicine, only looked for a signal of long-term symptoms. It is not known for how long those seeking help had struggled with the problems – it could have been days or weeks.
Nor was the severity of the symptoms documented. And the researchers acknowledged there was growing evidence that those who had fallen severely ill with Covid could have long-lasting and debilitating symptoms.
They said more research was needed into the issue of long Covid, but said the study did also shine a light on how little is known about persistent ill-health caused by flu.
„Long-term symptoms from flu have probably been overlooked before,” added Dr Max Taquet, another of the lead researchers.