Background The goal of this clinical trial is to learn if prednisolone works to treat moderate to severe respiratory tract infections in adults admitted to hospital. It will also learn about the safety of prednisolone in this context. The main questions it aims to answer are: Does prednisolone lower the number of participants who develop sepsis or who survive? What medical problems do participants have when taking prednisolone? Researchers will compare prednisolone to a placebo (a look-alike substance that contains no drug) to see if prednisolone works to treat respiratory tract infections in adults. Participants will: Take prednisolone 30mg or a placebo every day for 5 days. Complete a daily diary of symptoms for 30 days and have telephone follow up. Investigators propose to recruit 1300 patients, 650 in each group. The Trial will be conducted in the Emergency Departments and wards of hospitals in Hong Kong. Investigators expect the proportion of patients admitted to the hospital who develop sepsis or who die within 30 days to be reduced from 25% to 18% after taking active treatment. Secondly, investigators expect any difference in the proportion of patients with Serious adverse events(SAEs) not to exceed 5% between active treatment group and control. Benefits to Hong Kong and Worldwide: Active treatments (e.g. prednisolone are cheap, HK$0.2 per 5mg tablet) are widely available across the world. Any reduction of progression to sepsis and death if applied worldwide would improve the lives of millions of patients and save millions of dollars of healthcare costs.