Hello, again dear readers, and welcome to a bonus letters column. We’ve had a deluge of mail, so we’ll jump right in. -- We continue to get questions about COVID-19, which is clearly with us for the long haul. A reader in Long Beach, California, echoed several readers in wondering about the aftereffects of the illness. “Can having COVID-19 cause cognitive changes?” they asked. The answer is yes. People who have recovered from COVID-19, including those with mild illness, report ongoing changes to memory, attention, alertness and the ability to process new information. This is collectively referred to as “brain fog.” Some people also find they have an increase in anxiety and depression, as well as changes to sleep. In some cases, these resolve in the weeks after physical symptoms have ended. For some people who develop what is known as long COVID, the cognitive effects continue. The reasons for this are not clear, but both brain fog and long COVID are subjects of intensive research.