The coronavirus pandemic could last over 18 months, according to a 100-page federal government response plan recently shared with The New York Times.

The next year and a half could include “multiple waves of illness,” according to the document. “The spread and severity of COVID-19 will be difficult to forecast and characterize.”

What’s more, increasing COVID-19 cases in the U.S. will mean more hospitalizations among at-risk people, which could strain the health care system, they wrote. The document, dated March 13, is marked as “unclassified” but “for Official Use Only,” and “Not For Public Distribution or Release.”