Hmm I'm aware that lack of ventilation makes it more conducive for SARS-CoV-2 to spread, but not sure if it makes the disease more severe. Although it's hard to say without a control group for comparison, proper ventilation is generally advised to help reduce the spread.

https://www.who.int/news-room/q-a-detail/coronavirus-disease-covid-19-staying-at-hotels-and-accommodation-establishments