Even a mild COVID-19 infection can take a heavy toll on your cognitive health – severely affecting your memory and attention span, with effects lingering up to 18 months later, scientists say. According to a new study, conducted by the University of Sao Paulo, it is not just people who survived a severe bout of coronavirus infection that can be left battling "brain fog".

The study collected data from over 300 volunteers – all of whom had mild, moderate, and severe cases of COVID-19. Researchers said they assessed their IQ, attention, memory, processing speed, as well as symptoms of anxiety, stress, and depression, at least 18 months after they recovered.

The study's results revealed that all three groups reported lingering memory loss and concentration problems, as a result of long COVID-19.

According to experts, the study calculated symptoms of cognitive issues to be most severe in those who had a critical infection, with over 50 per cent reporting cognitive impairment. Nearly 39 per cent who had a moderate bout said they had residual impacts on their memory and attention. But 11.7 per cent of those who had minimal symptoms of COVID-19 still reported lingering cognitive impacts even months after recovering from their illness.

However, based on the study results, scientists said cognitive difficulties may diminish over time in milder cases. "We showed that cognitive symptoms persist in mild cases and are even more prevalent in individuals with severe manifestations," researchers wrote in the paper published in BMC Psychology. "Furthermore, we confirmed our central hypothesis: people with severe forms of COVID-19 show diminished cognitive performance 18 months after infection compared to those with mild to moderate forms," they added.

According to scientists, those with poor memory and attention said they faced severe difficulties in recalling words or performing routine activities like forgetting milk kept on the gas stove for boiling or even failing to pick children up from school.

Antônio de Pádua Serafim, study author and a professor at the Institute of Psychology, said: “Although the damage done by the disease in terms of memory loss, attention deficit, and slow processing increases in proportion to its severity, the same problems affect a far from negligible number of people - around 100 in our study - who had mild or moderate COVID."

According to experts, neuroinflammation – the inflammatory response in the brain triggered by infection causes memory problems after the COVID-19 infection. “Memory loss and attention deficit are known to be associated with post-intensive care syndrome due to intubation under deep anesthesia. Some of the data analyzed in the study, however, was from patients who didn’t require intensive care or didn’t even have sufficient symptoms to be hospitalized and nevertheless exhibited memory loss and attention deficit,” Prof Serafim added.

Long COVID is defined as a chronic condition that occurs after SARS-CoV-2 infection and is present for at least three months. Long COVID-19 includes a wide range of symptoms or conditions that may improve, worsen, or be ongoing.

Apart from memory issues, other common symptoms of long COVID-19 include: