Getting IRB approval retrospectively for study involving humans

r/Medicine,

Suppose that we have data collected over the past year from a patient population, and all patients consented to have their deidentified health information used for research purposes. We did not have IRB approval for a project at the time of data collection.

Is it possible to get IRB approval to retrospectively use this data for a study? Or, did we have to have IRB approval at the time of collecting the data to use it in a study?

Sorry if this is a silly question - I am rather unfamiliar with the IRB process, as in previous research projects, I joined the team after approval was already gained.

Thanks in advance for any response.