Recently, some parents responded that their children had a strong reaction to the fourth injection of Pepcid, that is, the booster shot, with symptoms such as persistent fever, pain and even coughing and irritability. The parents said that after three injections, there were no such serious symptoms and performance, how could there be such a big reaction to this fourth injection! First of all, let’s have a preliminary understanding of this diphtheria vaccine The diphtheria vaccine is actually not a vaccine to prevent one disease, it is a three-in-one vaccine for pertussis, diphtheria and tetanus, which is made from pertussis vaccine, refined diphtheria and tetanus toxoid, in the right proportion, and is a vaccine to prevent three diseases: pertussis, diphtheria and tetanus. The first dose is given when the child is 3 months old, with three consecutive doses, and then a booster dose, the fourth dose, is given before the child is 2 years old. In this way, the vaccine will be effective in preventing the disease. Don’t vaccines prevent diseases? Why are there adverse reactions? This has to do with the characteristics of the vaccine itself. Since the vaccine contains some adsorbent, the baby may have local redness, pain and itching after vaccination, hard nodules or sterile abscesses at the injection site, slight fever in the whole body, and may also be tired and irritable, etc. These symptoms are all normal reactions and can disappear on their own within a period of time, so parents need not worry too much. Some children, in the first three injections of the vaccination of Bai Bai Bao, there is no obvious discomfort reaction, but in the vaccination of the fourth injection, there is a more serious reaction, what is the reason? The fourth shot is a booster shot has a higher chance of reaction than the basic immunization, but the reason is not easy to explain. Parents can first observe, if the child continued fever, vomiting, poor spirit, etc., no signs of relief, to go to the hospital. Therefore, it is best to choose a time when the child is in good health to receive the booster shot, and the child’s health should be closely observed within 2 days after the vaccination.