A previously unknown outbreak of the Zika virus swept across Cuba in 2017, a year after the global health emergency was declared over, scientists reported on Thursday.

Until now, the Pan American Health Organization had no record of any Zika infection in Cuba in 2017, much less an outbreak. Following inquiries by The New York Times about the new study, published in the journal Cell, officials acknowledged that they had failed to tally 1,384 cases reported by Cuban officials that year.

That figure is a sharp increase over the 187 cases confirmed in 2016 and is “in line with the estimates for 2017 from our own study,” said Kristian Andersen, an infectious disease researcher at Scripps Research Translational Institute in La Jolla, Calif., and a co-author of the new study.

Because most cases of Zika go unconfirmed, Dr. Andersen added, the outbreak actually may have comprised tens of thousands of infections.