Strong interest in the George Zimmerman trial and improved performances for shows including “Anderson Cooper 360,” CNN is enjoying a ratings surge this summer — and has virtually caught up with or surpassed MSNBC in key categories.

Fox News remains the leader, as it has for years, though it and MSNBC were down vs. last summer.

In preliminary Nielsen data for the summer through Sunday, Fox News was averaging 1.85 million viewers in primetime (down 5% from comparable dates a year ago), followed among the news networks by MSNBC (540,000, down 22%), CNN (533,000, up 21%) and HLN (422,000, up 29%).

Among all cable networks in primetime this summer, Fox News ranks seventh in total viewers (USA and TNT top the list). MSNBC is 33rd, CNN is 34th and HLN is running 39th.

In the adults 25-54 news demo, it’s a closer four-network news race, with FNC on top (272,000), followed by MSNBC (186,000), CNN (178,000) and HLN (159,000).

CNN has seen primetime gains in all hours, with “Anderson Cooper 360” up the most (+27% in total viewers and +36% in adults 25-54).

Inside Man” with Morgan Spurlock launched on Sundays in the 10p hour at the end of June.  Through the first five premiere telecasts, the program increased Live+7 viewing in the time-period by 15% in total viewers and 63% in adults 25-54.

CNN has made strides in other day parts too under Jeff Zucker, including with new series “New Day” and “The Lead With Jake Tapper.” It is averaging 410,000 viewers this summer (up 28% from last year), ahead of MSNBC (354,000, down 17%) and HLN (321,000, up 34%) but drawing less than half of the overall numbers of FNC (1.05 million).

In adults 25-54 total day, Fox News (208,000, down 15%) is still comfortably on top, although both CNN (134,000, up 37%) and HLN (125,000, up 28%) have closed the gap.