The most common and most likely answer to this crossword clue is the 8 letter word SYSTEMIC
I've seen this crossword clue in The Guardian
S
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S
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Buddy explains!

The straight part
We know that "affecting an entire body" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case affecting an entire body = systemic.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SYSTEMIC mean?
SYSTEMIC adjective- Embedded within and spread throughout and affecting a whole system, group, body, economy, market, or society.
- Pertaining to an entire organism.