The monarch speaks about her experience with the virus during a virtual hospital visit.
Mr Hussain was the third member of his family to be admitted to hospital with the virus in December 2020. While he was there, his brother and father died.
Mrs Hussain told the Queen that at one point 500 friends and family from across the world were on a Zoom call praying for her husband. The monarch asked the couple: "So you have a large family, or a large influence on people?" "We held their hands, we wiped their tears and we provided comfort. It felt at times that we were running a marathon with no finish line."
About 800 people from across north-east London have so far been treated at the 155-bed Queen Elizabeth Unit. It was built in five weeks to meet the demand for Covid patients, instead of the normal time period of five months.