i know those lights! my grandma had them!

Wonderful (and vivid) imagery. I love the use of disease Rubella, as well as the, lights and tree descriptions that give this a nice “dated” (retro) feel.
The title of the story is the cherry on the sundae.

I really enjoyed this, and I agree with the “retro” feel and the title is funny.

who still has aluminium Christmas trees?

Retro, yes, this took place in 1971. Glad that you liked the setting (and some are old enough to remember it ;).

Really vivid description. Nicely done.

You’ve conveyed the feel of being unwell, and how fevers distort perspective, but all added a certain poignancy of being young and sick at a special time of the year.

Lovely little bit of story. I really liked the undertone of frightening that the spectacle holds for this little kid. Very nicely balanced and authentic.