For months, journalists and politicians fixated on the number of people signing up for health insurance through the federal exchange created as part of the Affordable Care Act. It turned out that more than 5 million people signed up using Healthcare.gov by April 19, the end of the open-enrollment period.

But perhaps more surprising is that, according to federal data released Wednesday to ProPublica, there have been nearly 1 million transactions on the exchange since then. People are allowed to sign up and switch plans after certain life events, such as job changes, moves, the birth of a baby, marriages and divorces.

The volume of these transactions was a jolt even for those who have watched the rollout of the ACA most closely.