What is the minimum interval required between a live vaccine and a PPD skin test?

The minimum interval required between administering a live vaccine and conducting a PPD (purified protein derivative) skin test is 28 days. This is essential because live vaccines, such as those for measles, mumps, rubella, and varicella, can potentially suppress the immune response, which may lead to a false negative result on the PPD skin test.

Administering a live vaccine too close to a PPD test could inhibit the body's ability to mount an appropriate immune response, thus skewing the results of the skin test, which is designed to evaluate immunity to tuberculosis. By allowing a minimum of 28 days between the administration of a live vaccine and the skin test, it ensures that the immune system has had sufficient time to respond optimally to the vaccine, thereby providing a more accurate result for the PPD test.