There are three occurrences of corporate healing in response to prayer recorded in the Old Testament.

1.  Numbers 16:46-50  Aaron stopped the plague which had killed 14,700 people by offering incense and making atonement for the people.

2.  Numbers 21:4-9  The Lord sent venomous snakes among rebellious Israel.  Moses prayed for them, made a bronze snake and anyone who looked at it lived.

3.  2 Samuel 24:10-25  David sinned by counting his troops and the Lord sent a plague upon Israel which took 70,000 lives.  David built an altar, sacrificed burnt and fellowship offerings and prayed to the Lord.  He answered and stopped the plague.