The expected BCG reaction
After bacille Calmette-Guérin (BCG) vaccination, a small raised papule usually appears at the injection site in about 2 to 3 weeks. It may become a small pustule or a shallow ulcer and then heals over weeks to a few months, leaving a small scar. This 6-week-old developed a bump 3 weeks after his birth vaccines, it has a small pus-filled center, and he is feeding well with no fever and no swelling in the armpit. This is the usual response to BCG, which heals with a small scar.
Why the reaction happens
BCG is a live attenuated vaccine given intradermally. The local reaction reflects the body's immune response to the vaccine organisms at the site, and it is a normal part of the vaccine's action. The scar that forms afterward is often used as evidence that the child received BCG, although the absence of a scar does not always mean the vaccine failed.
Care of the BCG site
The nurse teaches the mother to keep the site clean and dry and to leave it uncovered or loosely covered by clothing. Nothing is applied to the site, including antibiotic ointment, powder, or home remedies, and the pustule is not squeezed or punctured. The reaction will heal on its own. The mother is told to return if the swelling becomes large, if a lump appears in the armpit, or if the baby becomes unwell.
Why the other explanations are wrong
The pustule does not mean the vaccine failed; on the contrary, it shows the expected local response, so the vaccine is not repeated. It is not a BCG abscess needing drainage, because an abscess would be a larger, fluctuant swelling, and complications often involve enlarged lymph nodes in the armpit. It is not a local bacterial infection, so antibiotic ointment is unnecessary and inappropriate. Watch out! Parents may worry when they see pus, so the nurse explains in advance that a small pustule is expected.
Exam takeaway
A papule at 2 to 3 weeks that becomes a small pustule or ulcer and heals with a scar is the normal BCG reaction. Key point! Keep the site clean and dry, apply nothing, and refer only for a large abscess, spreading axillary lymph node swelling, or a sick child.