Adverse effects of the BCG vaccine

Expected normal reactions

The BCG vaccine will cause a small lump to appear at the vaccination site within two to six weeks. When the lump at the vaccination site bursts, the site may ooze for a few weeks and sometimes even longer. It usually heals within around two months, leaving a scar on the site.

If the injection site oozes, it should be covered with a dry dressing that allows air circulation. No other treatment is needed.

The vaccine often also causes slight enlargement of the lymph nodes closest to the injection site.  The enlarged lymph node is generally less than 1 cm in diameter and may be tender. The swelling of the lymph node usually disappears by itself.

Prolonged oozing or an abscess at the injection site

Sometimes the injection site may continue to ooze for months: the scab comes off several times and the oozing continues. An abscess may also develop at the injection site. Based on cases reported to the national register of adverse reactions to vaccinations, approx. 3 recipients out of 10,000 who have been administered the BCG Vaccine SSI product used in Finland have developed an abscess.

  • Cover the oozing injection site with a dry dressing that allows air circulation or a clean top.
  • You can clean the injection site when washing or bathing your baby as usual. There is no need to clean the site separately under the shower.
  • Prolonged oozing at the injection site does not usually require any other treatment, even if the oozing started afresh after subsiding for a time.

Secondary infections at the injection site are rare. If the ulcer becomes tender or redness spreads across a wider area, the secondary infection can be treated with a first generation cephalosporin.

An abscess at the injection site should be treated similarly to an abscess on the regional lymph node.


The bacteria in the BCG vaccine may sometimes cause a slowly developing infection and enlarge the lymph node near the injection site. When the vaccine is administered in the upper arm, the lymph node reaction is most likely to occur in the armpit, and less often above the collarbone or in the neck.

The inflamed and enlarged lymph node is usually 2 to 4 cm in diameter. In most cases it is observed 3 to 7 months after the vaccination. It also takes time to heal. It usually takes several months for the lymph node to reduce in size, and it may remain palpable for years.

No specific treatment is required, and monitoring the situation is enough. In a child who has no chronic illnesses, lymphadenitis does not increase the risk of infections at remote sites, such as osteitis and arthritis (inflammation in bones or joints).

Lymph node abscess

Lymphadenitis sometimes develops into a festering abscess. The national register of adverse reactions to vaccinations shows that the Danish BCG vaccine causes a festering inflammation in the inguinal lymph node in 1 to 2 cases per 1,000 vaccine recipients when the vaccine is administered in the thigh. Once administration in the upper arm was introduced, the incidence of lymph node abscesses stabilised.

The abscess may rupture, in which case pus drains out. Oozing may continue for several weeks or even months. The ulcer will heal by itself from the bottom up.

  • Once the abscess has burst, squeeze it lightly every day to expel the pus.
  • You can clean the abscess site when washing or bathing your baby as usual. There is no need to clean the site separately under the shower.
  • No local antiseptics are needed.
  • If the ulcer is oozing heavily, it can be covered with a folded dressing. When the oozing is reduced, it is enough to put on the child a clean top, which should be washed at 60 degrees with other baby laundry.
  • The child should be kept away from swimming pools while the oozing continues.

If the child is otherwise healthy, no further examinations or other specific treatments are required. If the problem becomes prolonged and the ulcer continues to ooze for more than four months, you should contact a specialist in paediatric infectious diseases.

Rare infections at remote sites

In rare cases, the bacteria in the BCG vaccine may cause an infection at a site away from the vaccination site. These so-called remote infections include:

  • bone or joint inflammations (osteitis or arthritis)
  • a subcutaneous abscess or a BCG infection on the skin
  • a disseminated BCG infection.

When using the Danish BCG vaccine, such adverse reactions have been observed in approx. one child per 7,000 vaccine recipients.  Most of these cases have been bone inflammations caused by the vaccine bacteria. The incubation period of remote site infections diagnosed in Finland has been on average 14 months (ranging from 2 to 26 months).

Disseminated BCG infections following a vaccination are extremely rare. The risk of a healthy child developing a disseminated BCG infection is very low. In these cases, there usually is some other underlying and undiagnosed illness or condition that weakens the body’s immune defence. In a child with severe immunodeficiency, the BCG vaccination can cause a serious and even fatal disseminated infection. These infections affect approx. one child per 100,000 vaccine recipients.

Remote infections caused by the BCG vaccine are always diagnosed and treated in specialised medical care.

An adverse reaction report must always be submitted for serious adverse reactions.