I can vouch for this and say "yep, absolutely."

When the immune system is diminished, I'd say ALL systems are diminished, so any avenue that a neg could possibly use to gain entry, is left more vulnerable. "Forced entry" type attacks are more likely to break through one's natural defenses (and more likely to be attempted if they have a better chance at working), and more manipulative, "nudge you in their direction" type stuff is also more effective on a system thats already out of balance.

So, keep scarfing those Flintstone vitamins, kids.