The hospital was set up at Warsaw's National Stadium, a prime venue for sports and entertainment events next to the Vistula river. It started admitting patients late last year.
The Polish prime minister's top aide, Michał Dworczyk, who is spearheading the country's inoculation drive, said on Wednesday that the facility had provided help to more than 1,800 people, and a quarter of a million COVID vaccinations had been administered there.
Dworczyk added that it would be possible to rapidly reactivate the hospital if coronavirus cases soared again and Poland was hit by a fourth wave of the epidemic.
Officials on Wednesday reported 2,344 new coronavirus infections, down from a high of 35,251 single-day cases on April 1.
A total of 11.87 million Poles have received their first doses of COVID-19 vaccines, while almost 4.8 million people have been fully inoculated, according to the health ministry.