Doctors looked at data from many different studies involving about one point eight million children. They wanted to know how often the BCG vaccine caused swelling in the lymph nodes. The rate of this side effect was not the same in every single study. It went from zero percent all the way up to twenty five point six percent. This big difference makes it hard to give one simple number for how common the problem is.
The way doctors looked for the swelling made a huge difference in the results. When studies used active checking, they found more cases than when they just waited for parents to call. Also, the type of study design mattered. Some studies that compared groups directly found higher rates than others that just watched over time. The specific brand of vaccine used also played a role in the numbers reported.
Because of these many differences, it is difficult to say exactly how often this happens. The review shows that the answer depends on many factors like the vaccine strain and how the study was done. This means doctors and parents need to understand that the risk is not the same everywhere. It is important to look at the specific situation when talking about vaccine safety.
