In the majority of infants a raised nodule develops at the site of the immunisation after 2 to 4 weeks. A small crust may develop or it may ulcerate. The nodule will heal by itself and no dressing should be applied. After 8 weeks the nodule starts to decrease in size and by 6 months a small flat scar will form. The lymph nodes in the axilla on that side may enlarge slightly, which is normal. BCG immunisation does not always leave a scar in an infant. It is not necessary to repeat the BCG immunisation if no scar is seen.
The most common side effects are local pain and ulceration at the site of the immunisation and enlarged lymph nodes in the axilla and sometimes the neck.
Serious side effects which require referral are very rare. They include:
- An abscess may form at the site of the immunisation.
- Axillary lymph nodes may enlarge rapidly to more than 3 cm.
BCG lymphadenitis or local abscess must be reported to the local health authorities. Rarely suppurative adenitis may require needle drainage or a sinus may form. Antituberculous treatment is seldom needed (usually in immunocompromised children only).