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A terrible pestilence was spreading through Italy at the time. The first symptom was severe, chronic sneezing, and this was often
quickly followed by death.
Pope Gregory urged the healthy to pray for the sick, and ordered that light-hearted responses to sneezes such as "May you enjoy good health" be replaced by the more urgent "God bless you!" If a person sneezed when alone, the Pope recommended that they say a prayer for themselves in the form of "God help me!" LiveScience
Then he returned, and walked in the house to and fro;
and went up, and stretched himself upon him:
and the child sneezed seven times,
and the child opened his eyes.
2 Kings 4:35
..No record here of saying "God Bless You" in Scripture due to a sneeze