Level 1: Definition and symptoms of pneumonia Pneumonia refers to lung infection caused by bacteria, viruses, fungi, etc. Two-month-old babies often show the following symptoms after contracting pneumonia: cough, fever, shortness of breath, loss of appetite, physical weakness, etc. Timely medical treatment is required. Level 2: Reasons why two-month-old babies are susceptible to pneumonia. Two-month-old babies have not fully developed their immunity and have weak resistance to bacteria and viruses, making them susceptible to infection. In addition, air pollution, unhygienic home environment, etc.