A Christmas pun has Santa Claus coming down with the flu(e). A riddle was posted on a 1996 book:
 
Q: What sickness did Santa get going down the chimney?
A: The flu (flue).
 
“Santa came down with the flue” was posted on the website Pun of the Day on January 25, 2017.
 
   
Wikipedia: Flue
A flue is a duct, pipe, or opening in a chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. Historically the term flue meant the chimney itself. In the United States, they are also known as vents for boilers and as breeching for water heaters and modern furnaces.
       
Google Books
Funniest Riddle Book in the World
By Morrie Gallant
Illustrated by Sanford Hoffman
New York, NY: Sterling Publishing Company Inc.
1996
Pg. 67:
What sickness did Santa get going down the chimney?
The flu (flue).
 
Google Books
3650 Jokes, Puns, and Riddles
By Charles Foxgrover, Anne Kostick and Michael J. Pellowski
Black Dog & Leventhal Publishers, Inc.
1998
Pg. 453:
Why did Santa visit his doctor before Christmas?
Because he always gets a flue shot before he slides down chimneys.
   
20 December 2008, Newsday (Long Island, NY), Kidsday sec., pg. B2:
Why did Santa start sneezing as he went down the chimney?
He caught a nasty flue.
Kimberly Rodriguez
 
Twitter
Santa and 2 others liked‏
@clove
We haven’t opened any gifts yet! We need Dr. House up in here. Cause Santa came down the flue and gave this house the flu.
11:53 AM - 25 Dec 2009
     
Twitter
Mo Cox‏
@comor94
What kind of disease does Santa get?
6 y/o cousin: “Chimney flue!”
10 y/o cousin: “Diabetes.”
5:41 PM - 25 Dec 2012
 
Twitter
Stephanie‏
@Saitisntso
I heard Santa came down with the flue.  Hope Santa has chimney insurance.
8:46 AM - 23 Dec 2013
     
Twitter
Ian Jackson‏
@Ianmaxijackson
Q. Why is Santa always sick at Christmas
A. He keeps getting caught with the chimney flue
6:11 AM - 24 Dec 2014
 
Twitter
Taaffe‏
@TarnTerrier
...... And finally an update to a previous attempted joke…..
Why did Santa go to the doctors?
He came down with chimney flue!
5:55 PM - 1 Jan 2016
 
Twitter
Seb Wake‏
@Seb_Wake
Q: Why did santa feel awful after Christmas?
A: He came down with the flue #badxmasjokes #badjokefriday
8:09 AM - 23 Dec 2016
     
Pun of the Day (January 25, 2017)
Santa came down with the flue.
Category - Working Outdoors
Submitted by - Joseph Leff - Brooklyn, NY
 
Twitter
Michael Grace‏
@RFYDNorg
January 25, 2017 - Santa came down with… - Santa came down with the flue. Comment On This Pun! http://ow.ly/z80g508VNvp
6:03 AM - 25 Jan 2017
   
Reddit—Oneliners
Santa came down with the flue.
submitted October 25, 2017 by wonliners
 
Reddit—Jokes
Why was Santa Claus sick?
submitted December 3, 2017 by LWrayBay
He came down with the flue.