The research found that nearly two-thirds of people over 65 who were hospitalized with the virus went on to suffer cognitive decline, which can be a precursor for dementia, weeks and months after the infection cleared.

Independent experts told DailyMail.com this is a trend they're watching closely, since if there is a link, it could affect the millions of older adults who were infected with the virus.

CDC data shows that over-65s accounted for nearly half of hospitalizations in the first two years of the pandemic, or roughly 1.7m people. The new study stops short of concluding that COVID and dementia are definitively linked, but experts described the evidence as 'compelling'. 

The researchers from the University of New South Wales reviewed 18 older studies as part of their paper. 

It is available as a pre-print in the journal Ageing Research Reviews, which means that is has yet to be reviewed by other scientists.

The review looked at about 412,900 participants hospitalized with COVID-19 and 411,900 healthy participants - both groups only involved people over age 65. They included data from Europe, North America and Asia. 

Most of the studies included in the review looked at trends from 2020 and 2021, before vaccinations were made widely available. Most of the studies also focused on individuals who were severely sick with the condition.

The studies didn't report vaccination status, what strain of COVID the patients had or whether they used personal protective equipment. 

They were tested for their brain health by taking cognitive assessments which measure an individual's memory, attention span, language skills, spatial orientation and visual skills, in both written and verbal formats.