In-Depth: What an intelligence test reveals about COVID brain fog Severe COVID linked to a 7-point drop in IQ COVID-19's impact on intelligence test and last updated 2021-07-28 21:43:01-04 SAN DIEGO (KGTV) -- A study using data from an online intelligence test offers new insight into the brain fog reported by so many COVID long haulers. Months after infection, people who recovered from COVID scored lower than their peers on tests designed to measure memory, reasoning, and problem solving, according to a study published by The Lancet. People who had the most severe symptoms had the largest declines. Those hospitalized and put on a ventilator had an average drop in cognitive scores equivalent to a 7-point decline in IQ, the researchers reported.