Spain's army expects there to be two more outbreaks of the coronavirus, according to an internal report seen by the Associated Press.
The army report predicts "two more waves of the epidemic" and that Spain will take "between a year and a year-and-a-half to return to normality."
The document was published by Spanish newspaper ABC on Friday and later confirmed as authentic by the AP.
"There will be a second wave of COVID-19" in the northern autumn or winter the army report said, adding that it will be less serious than the initial outbreak due to higher immunity in the population and better preparations.
It said that a "possible third wave would be greatly weakened" next year if there is a vaccine available.
The report was produced by the army as its own forecast of the pandemic, which it can share with civilian authorities. Spain's government has its own experts who make the final decisions on health policy, taking into account the opinion of other institutions and outside experts.
Spanish Prime Minister Pedro Sanchez has warned that he considers it highly probable that the virus will make comebacks until a vaccine is developed.
Health officials in Spain are carrying out a epidemiological survey to determine the extent of the contagion, including the several thousand people who have been mildly ill with cough and high fever but never been tested in a hospital.
There are also believed to be thousands more who were infected but never showed symptoms.
On Friday, the health ministry said that medical workers had taken blood samples from more than 46,000 people over the first week of the survey. It plans to test 60,000-90,000 overall.
More than 26,000 Spaniards are known to have died from the COVID-19 virus. Spain has gained control over the outbreak which has infected a confirmed 260,177 people in the country and is now easing restrictions to activate its battered economy.
When considering steps to prepare for the coming months, the army report said "it would be extremely important" to develop a contact tracing method using mobile phone applications. Spain so far has not done that and is relying on a local network of public health clinics to monitor future cases.