Deaths from opioids in the United States dropped by 5 percent between 2017 and 2018, but an analysis released Friday by the Rockefeller Institute says a celebration may be premature.

The analysis found there are reasons to be optimistic about the decrease, but the results from the Centers for Disease Control may be provisional.

At the same time, research is only one data point and it’s unclear if the decline will continue. Overdose deaths leveled off in 2012, for example, only to increase the following year.

And opioid-related deaths may be underreported due to flawed data collection, such as incomplete death certificates.

“These new data from the CDC offer hope,” said Rockefeller Institute Interim Executive Director Patricia Strach. “While acknowledging these successes is important, it is also important to remember that the fight isn’t over. Federal and state officials must continue their efforts to maintain these results in the future.”