How long should I wait to perform a tuberculin skin test after receiving the MMR vaccine?

Timing of Tuberculin Skin Test After MMR Vaccination

If you need to perform a tuberculin skin test (TST) after MMR vaccine administration, wait at least 4 weeks (preferably 4-6 weeks) before placing the TST, or ideally administer both on the same day with TST reading at 48-72 hours. 1, 2, 3

Optimal Timing Strategy

The best approach follows this algorithm:

First-line option (preferred):

• Administer the TST and MMR vaccine on the same day 1, 2
• Read the TST at 48-72 hours, before any vaccine-induced immunosuppression occurs 1, 2
• This ensures the person receives measles protection while obtaining accurate TST results 1

If MMR was already given:

• Wait at least 4 weeks after MMR vaccination before placing the TST 1, 3
• The FDA label for MMR vaccine specifically states the TST should be administered "before, simultaneously with, or at least 4 to 6 weeks after vaccination" 3
• This delay removes concern about transient suppression of TST reactivity from the vaccine 1

Least preferred option:

• Perform and read TST before administering MMR vaccine 1
• This delays measles protection and should only be used when same-day administration is not feasible 1

Why This Timing Matters

Immunologic mechanism:

• Live attenuated measles vaccine can theoretically suppress delayed-type hypersensitivity reactions, including TST reactivity 1, 3
• This immunosuppression can cause false-negative TST results if testing occurs during the suppression window 1, 2
• The degree of suppression from vaccine is likely less than from wild-type measles infection, but still clinically significant 1

Duration of suppression:

• Vaccine-induced immunosuppression begins shortly after vaccination 2
• The suppression can persist for 4-6 weeks 1, 2, 3
• Testing during this 1-4 week window is the peak period for false-negative results 2

Extension to Other Live Vaccines

This guidance applies to all live-attenuated viral vaccines:

• Varicella vaccine 1
• Yellow fever vaccine 1
• Smallpox vaccine (requires 4-week delay) 1
• No specific data exist for these vaccines, but following measles vaccine guidelines is prudent 1

Alternative Testing Option

If timing is problematic:

• Consider using an interferon-gamma release assay (IGRA) instead of TST 2
• IGRAs are not affected by live vaccines and require only a single visit 2, 4
• This is particularly useful when TB screening is urgent and cannot wait 4-6 weeks 2

Common Pitfalls to Avoid

Critical timing errors:

• Never place a TST 1-4 weeks after MMR vaccination - this is the peak immunosuppression period and will likely yield false-negative results 2
• Do not delay necessary MMR vaccination just to perform TST first, unless there is high clinical suspicion for active tuberculosis requiring immediate evaluation 1, 2
• Do not confuse this 4-6 week vaccine timing with the 8-10 week window for TB exposure testing, which is a completely different concept 2, 5

Documentation issues:

• Ensure proper documentation of vaccination dates to avoid inappropriate TST timing 2
• If TST was inadvertently placed during the suppression window, repeat testing after the appropriate interval 1

Special populations:

• Persons with untreated active tuberculosis should have antituberculosis therapy initiated before receiving MMR, as measles vaccine might theoretically exacerbate tuberculosis disease 1
• TST reactivity itself (in absence of active disease) is not a contraindication to MMR vaccination 1