The performance of prime RMBS  from 2005 to 2008, while better than other types of RMBS from that timeframe, has deteriorated at a faster pace, according to DBRS.

"The deterioration was particularly alarming in the last 12 months," said the rating agency. For example, DBRS data show between December 2008 and December 2009 the subprime sector saw a 12% increase in serious delinquencies while prime RMBS saw serious delinquencies ramp up by 47%.

However, the prime sector continues to have the lowest level of overall defaults and expected losses among RMBS sub-types, the rating agency said.

In addition, prime fixed rate mortgages generally have a much better track record when it comes to serious delinquencies than adjustable-rate mortgage product.

"Measured by the latest serious delinquency rates, fixed-rate prime mortgages on average performed 40% better than their ARM counterparts," the rating agency said.

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