Continued stress in the prime non-agency MBS sector, rising delinquencies and the use of a new loan-level loss model have prompted Fitch Ratings to revise loss expectations for more than 40 percent of non-agency pools backed by prime mortgage loans. A recent review of 1,154 rated transactions backed by prime collateral, consisting of approximately 15,000 bonds, caused Fitch to affirm or upgrade an estimated 58 percent of the prime non-agency MBS portfolio and to downgrade the remaining 42 percent, according to a report by the rating agency. At least 60 percent of the downgraded MBS were rated...