Perhaps someone should inform them that simply being around other women (vaccine or not) effects menstrual cycles.
en.wikipedia.org
You didn't read that wikipedia article, did you?
"After the initial studies, several papers were published reporting methodological flaws in studies reporting menstrual synchrony including McClintock's study. In addition, other studies were published that failed to find synchrony.
A 2013 review concluded that menstrual synchrony likely does not exist.
After the initial studies reporting menstrual synchrony began to appear in the scientific literature, other researchers began reporting the failure to find menstrual synchrony.
More recent studies, which took into account some of these methodological criticisms, failed to find menstrual synchrony.
"In light of the lack of empirical evidence for MS [menstrual synchrony]
sensu stricto, it seems there should be more widespread doubt than acceptance of this hypothesis"'