Q: Why has my article's status changed to "Reviewers assigned" after two days of "Under review"?

Detailed Question -

I submitted to Parasites & Vectors and the status changes were as follows:

Nov 26: new submission
Nov 27: editor assigned
Nov 29: editor assigned
Dec 03: under review
Dec 04: reviewers assigned

Why did the status change to "Reviewers assigned" after two days of "Under review"? Did the reviewer reject the review invitation so that editor had to look for a new reviewer? Or does "Under review" refer to the internal screening and not peer review?

1 Answer to this question
Answer:

From the status changes, it seems that "Under review" refers to the initial editorial screening. It takes some time for the editor to find reviewers, send out review invitations, and receive acceptance of the invitation from reviewers. Two days is too short a time for the editor to complete all of this. Moreover, the status before "Under review" was "Editor assigned" and not "Reviewers assigned." This makes me inclined to think that in this case, "Under review" refers to the internal screening by the editor. 

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