“I had to fly across the country for my vaccine, and, wow, are my arms sore”

“I just flew in and boy, are my arms tired!” is a very old joke (1940s). The arms are tired from flapping so much (like a bird’s wings).
 
A variation of the joke was posted on Reddit—Oneliners on April 16, 2021:
   
“I had to fly across the country for my vaccine, and, wow, are my arms sore.”
 
The arms are sore not only from the flapping, but from the vaccination. “I had to fly to London for my vaccine, and, wow, are my arms sore” was posted on Twitter by THS | OtmShank later on April 16, 2021.
 
     
Wikipedia: COVID-19 pandemic
The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first identified in December 2019 in Wuhan, China. The outbreak was declared a Public Health Emergency of International Concern in January 2020 and a pandemic in March 2020.
 
Reddit—Oneliners
Posted by u/SprawlingKeystrokes April 16, 2021
I had to fly across the country for my vaccine, and, wow, are my arms sore.
COMMENTS
Alex13104
I don’t get it, could you please explain
OscarTheFudd
his arms are sore because he was flying (by flapping his arms)
SprawlingKeystrokes
It’s a play off an old joke.
You’re arm gets sore after getting the vaccine. But the implication here is that I may have flown by flapping my arms, and that’s why they’re sore instead.
 
Twitter
THS | OtmShank
@0tmshank_
I had to fly to London for my vaccine, and, wow, are my arms sore.
5:15 PM · Apr 16, 2021·Twitter Web App