If your baby starts to have phlegm in his throat after vaccination, consider that it may be a side effect of the vaccine or an upper respiratory tract infection may occur. If the baby is unwell, it is recommended to go to the hospital for examination in time and cooperate with the doctor for treatment.1. Side effects of vaccines: After vaccination, the baby may have slight fever, cough, phlegm, abdominal distension, indigestion and other adverse reactions, which can lead to the baby starting to have phlegm in the throat after vaccination, usually with mild symptoms, usually lasting about a week. It is suggested that parents should give the baby some light and easily digestible food, pay attention to keeping the baby warm, take more rest, observe the baby’s condition, and take the baby to the doctor in time if the symptoms do not ease; 2. Upper respiratory tract infection: If the baby is infected with bacteria, virus and other pathogens within a period of time after vaccination, symptoms such as cough, runny nose, congestion, coughing and cold, along with symptoms such as general body aches and weakness, may also lead to phlegm in the throat after vaccination. The vaccine can also lead to phlegm in the throat. Parents are advised to take their babies to the hospital for examination in a timely manner. If upper respiratory tract infection clearly appears, the baby can be treated with drugs such as dextromethorphan hydrobromide syrup and busulfan anti-inflammatory oral solution under the guidance of the doctor to relieve the symptoms.