Use a variable between workbooks

Code in workbook1

Public data_feed_active As Boolean


Sub send_data()
data_feed_active = True
Workbooks.Open second_work_book, ReadOnly:=True
End Sub

Code in second workbook

Sub Workbook_open()
If data_feed_active = True Then Exit Sub
Call setup
End Sub

What I want to happen is Setup will only be called if the the workbook has not been opened by the first workbook.

However data_feed_active in the second workbook is empty