What Is the BCG Vaccine?

The BCG (Bacille Calmette-Guérin) vaccine is a vaccine against tuberculosis that is routinely administered in many countries, particularly in regions where TB is prevalent. It is commonly given at birth or in early childhood in countries throughout Asia, Africa, Latin America, Eastern Europe, and elsewhere.

The BCG vaccine is not routinely given in the United States. As a result, many immigration applicants from other countries have received BCG vaccination, which historically created complications with TB skin test interpretation.

Why BCG Caused Problems With the TB Skin Test

The traditional TB skin test (TST/Mantoux) works by measuring the skin's reaction to tuberculin protein. Because the BCG vaccine contains live attenuated TB bacteria, it can prime the immune system to react to tuberculin — causing a positive skin test result even in people who have never been infected with TB.

This cross-reactivity between BCG vaccination and the TB skin test was a significant problem for immigration medical examinations, as it led to many false-positive results among applicants from countries where BCG is routinely given. These false positives required additional evaluation and caused unnecessary delays.

Why the IGRA Blood Test Is Not Affected by BCG

The IGRA blood test (QuantiFERON-TB Gold Plus) uses specific TB antigens — ESAT-6 and CFP-10 — that are present in Mycobacterium tuberculosis (the TB bacterium) but are absent from the BCG vaccine strain and most non-TB mycobacteria. This means the IGRA test specifically detects immune responses to actual TB infection, not responses triggered by BCG vaccination.

As a result, prior BCG vaccination does not cause a false-positive IGRA result. This is one of the primary reasons USCIS and the CDC adopted the IGRA as the preferred TB screening method for immigration medical examinations.

What to Tell Our Civil Surgeon About Your BCG Vaccination

You should inform our civil surgeon if you received the BCG vaccine, even though it will not affect your IGRA test result. This information is part of your medical history and may be relevant to the overall interpretation of your TB screening. If you have a BCG vaccination scar (typically on the upper arm or shoulder), our civil surgeon may note this during the physical examination.

• Inform the civil surgeon of your BCG vaccination history
• Bring your vaccination records if available
• Note the approximate age at which you received BCG
• The IGRA blood test will not be affected by your BCG vaccination

Countries Where BCG Is Routinely Administered

BCG vaccination is part of the routine childhood immunization schedule in many countries, including but not limited to: Brazil, China, India, Mexico, the Philippines, South Korea, Russia, most African nations, and many countries in Southeast Asia and Eastern Europe. If you were born or raised in any of these regions, you likely received BCG vaccination. Rest assured that this will not affect your immigration TB blood test results.