The actor and cartoonist chose to name her new baby after the Liverpool goalkeeper Alisson Becker.
The actress best known for playing Lavender Brown says COVID-19 has hit her "like a ton of bricks for weeks."
The actor and cartoonist already has three children with her partner, comedian Alfie Brown.
Baby Tenn was in hospital as he tested positive for the coronavirus.
The actor and cartoonist introduced her baby boy to her Instagram followers.
The actress is known for playing Lavender Brown in the 'Harry Potter' films.