How long after a Mantoux (tuberculin skin test) can the BCG (Bacillus Calmette-Guérin) vaccine be administered?

Timing of BCG Vaccination After Mantoux Test

BCG vaccination should be administered only after confirming a negative Mantoux test result (induration <5mm), typically waiting at least 3 days after reading the Mantoux test. 1

Rationale for Timing

The timing between a Mantoux tuberculin skin test (TST) and BCG vaccination is critical to ensure accurate interpretation of test results and proper administration of the vaccine. This timing is based on several key principles:

1. Confirmation of TB-free status: BCG is only given to individuals who have a negative tuberculin skin test (induration <5mm), confirming they are not already infected with TB 1

2. Test reading requirements: The Mantoux test must be read 48-72 hours after administration to accurately assess for TB infection

3. Avoiding interference: BCG vaccination after a positive Mantoux test could complicate management of potential TB infection

Protocol for BCG Administration After Mantoux Testing

Step 1: Mantoux Test Administration and Reading

• Administer the Mantoux test using 5 TU of PPD tuberculin
• Read the test result at 48-72 hours
• Document the result in millimeters of induration

Step 2: Decision Based on Mantoux Result

• If Mantoux test is negative (<5mm induration):

  • Proceed with BCG vaccination
  • Can be administered immediately after confirming the negative result (typically day 3 after Mantoux administration)

• If Mantoux test is positive (≥5mm induration):

  • BCG vaccination is contraindicated
  • Further evaluation for TB infection or disease is required
  • Consider chest radiograph and possible TB prophylaxis or treatment 1

Special Considerations

For Children Without Prior BCG

• If the initial Mantoux test is negative (Heaf grade 0-1), BCG can be administered after confirming the negative result
• For children with continuous TB exposure risk, a repeat Mantoux test at 6 weeks may be required before BCG administration 1

For Neonates

• Newborns of mothers with smear-positive TB may receive isoniazid chemoprophylaxis for 3 months
• After 3 months, if Mantoux test is negative and mother is no longer infectious, BCG vaccination can be given 1

Common Pitfalls to Avoid

1. Administering BCG without confirming Mantoux results: Always ensure the Mantoux test is properly read and documented before BCG administration

2. Giving BCG to individuals with positive Mantoux tests: This can complicate future TB screening and management

3. Delaying BCG unnecessarily: While confirmation of a negative Mantoux is essential, once confirmed, there's no benefit to further delay in administering BCG

4. Ignoring contraindications: BCG should not be given to immunocompromised individuals, including those with HIV infection, regardless of Mantoux results 1, 2

BCG vaccination remains an important tool for TB prevention in specific populations, particularly for preventing severe forms of TB in children. However, proper timing and protocol following Mantoux testing are essential for its safe and effective use.