The novel coronavirus circulated in January in California, weeks earlier than thought, and early deaths were likely mistaken for the flu, a county health official said on Wednesday.

A 57-year-old woman had died of COVID-19 on Feb. 6, far earlier than any other reported cases in the United States, said Sara Cody, the health officer in Santa Clara County, California.

It was previously thought that the first U.S. death from COVID-19, the respiratory disease caused by the virus, was in Washington state on Feb. 29.

News of the deaths in California could improve public health officials’ understanding of how the outbreak took hold in the United States.

Additional early deaths may also be discovered in California, further changing public health officials’ understanding of the virus’ progress. On Wednesday, Governor Gavin Newsom said that he had asked medical examiners from all 58 counties in California to research deaths that might have been COVID-related back to December.

“What these deaths tell us is that we had community transmission probably to a significant degree, far earlier than we had known, and that indicates that the virus was probably introduced and circulating in our community far earlier than we had known,” a health official said.

Because the region was undergoing a bad flu season at the time, many cases may have been misclassified as influenza, as per the health official.

The cases were likely “iceberg tips,” health official said, indicating that many more people were also infected.