Which word do you have an issue with in the NYT headline, 'reaction'? As in, the 'adversity' faced by this patient may not in fact be a 'reaction' to the vaccine?
The NYT makes the headline about an adverse reaction and the study is paused because of it. To my mind 'adverse reaction' means that they've established the cause and effect, and the study was halted because someone reacted badly to the vaccine.
My issue is that it's not clear whether the patient's illness is due to the vaccine or something else, so headlining with 'adverse reaction to the vaccine' is jumping to a conclusion. They don't say 'possible', which is the truth.
The use of "halted" in the NYT headline commonly means stop or end.
halted; halting; halts Definition of halt
(Entry 1 of 4)
intransitive verb
1 : to cease marching or journeying
2 : discontinue, terminate the project halted for lack of funds
transitive verb
1 : to bring to a stop the strike halted subways and buses
2 : to cause the discontinuance of : end halt hostilities
https://www.merriam-webster.com/dictionary/halt
on hold in American English
1. in a period or state of interruption or delay the countdown was on hold
2. in a state of interruption in a telephone call, as during a transfer to another line I was on hold for five minutes
https://www.collinsdictionary.com/us/dictionary/english/on-h...