Virtually everyone who has a BCG vaccination will develop a raised blister at the site of the injection immediately afterwards. This is normal and nothing to worry about.
BCG injection scar
Two to six weeks after the injection, a small spot may appear at the site of the injection. It can grow into a circle up to 7mm across and may become crusty where fluid has dried on the surface.
The spot can be painful and bruised for a few days, but will eventually heal. It usually leaves a small scar.
Occasionally, there may be a more severe skin reaction, but this should heal within a few weeks.
If you are worried that you or your child's skin reaction is abnormal or that the spot may have become infected, contact your GP.
Allergy to the BCG vaccine
Serious side effects to the BCG vaccine, such as an anaphylactic reaction (a serious allergic reaction), are very rare. They occur in less than one in a million cases.
All staff who give vaccinations are trained to treat allergic reactions. Anyone who has an allergic reaction to a vaccine recovers completely with no lasting effects if they're treated promptly.
To find out more, read Vaccine safety and side effects.
Find out how to report a vaccine side effect.
Read more about the BCG vaccine.
Article provided by NHS Choices