The end of open enrollment for public health exchanges brought sweeping, rapid change. Even in late March, the 7 million enrollees once predicted by the Congressional Budget Office seemed like a pipe dream, and the Obama administration had set lower expectations. After February enrollment brought the tally to just 4.2 million enrollees, the more modest goal of 6 million became a longer shot.

Then in mid-March, enrollment passed 5 million. Suddenly, 6 million enrollees seemed within reach. Four days before the deadline, 6 million became reality, and the 7 million milestone announced on April 1 surprised nearly all exchange watchers.

How those 7 million lives break down remains unclear. The four biggest states California, Texas, Florida and New York will claim the lion's share of enrollment. Less populous states from Idaho and Montana to Maine, New Hampshire and Rhode Island largely met or surpassed their exchange goals, but those states represent a drop in the overall enrollment bucket.

What triggered the rush. A month of intense outreach in most states helped. The President's appearance on Between Two Ferns with Zack Galifianakis likely helped more.

Maybe March 31 is just the new April 15. The lines waiting for Connect for Health Colorado's retail store in downtown Denver looked awfully similar to the post office lines of mid-April. Picking a health insurance plan might be distasteful, but when a deadline looms, people will sign up.

The extended deadline for stuck-in-enrollment limbo will likely boost the final figure further, as will any leftovers from state-run exchanges that saw last-minute enrollment surges (California and New York, most notably). Sure, a number of people won't pay premiums and will fall off the rolls. The impact of exchange enrollment on uninsured rates is also unknown. It will depend on how many people already had individual coverage and found a better deal in the exchange.

Healthcare.gov came a long way in a short time. The online marketplace was a laughingstock in October and November, when website problems limited enrollment to just 137,000 people nationwide, but a technology revamp turned the troubled website around. Several beleaguered state-run exchanges did not see such a startling reversal of fortunes and largely limped to the end of open enrollment. One of those is run by Maryland, which just adopted the Access Health CT model as a replacement for its own failed exchange. It won't be the last.

What do 7 million lives mean for insurers? In addition to a bigger pool of enrollees, a few winners will emerge. WellPoint and state-based nonprofit Blue plans will likely end up in that column. Measuring success for regional plans and other non-profit insurers is more difficult. Cigna estimates it will add between 75,000 and 100,000 enrollees, two-thirds of them from the five state exchanges where it sells plans (Arizona, Colorado, Florida, Tennessee and Texas). Where CO-OPS priced competitively or offered broader networks, they captured bigger portions of exchange enrollees. Where they didn't, incumbent plans reigned.

No carrier or exchange will have much time to bask in open enrollment success. Insurers that want to sell exchange plans for 2015 must file their rates by the end of May. In less than two months, insurers must get a handle on the demographics and health status of their exchange populations. That might require a bigger miracle than meeting an unexpected exchange enrollment goal.

Follow Bill Melville on Twitter @BillMelvilleDRG

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