When not given on the same day, is the interval between yellow fever and MMR vaccines 4 weeks (28 days) or 30 days? I have seen the yellow fever and live virus vaccine recommendations published both ways.

The “General Best Practice Guidelines for Immunization” (see www.cdc.gov/vaccines/hcp/acip-recs/general-recs/timing.html) makes the generic recommendation that live parenterally or nasally administered vaccines not given on the same day should be separated by at least 28 days. The CDC travel health website recommends that yellow fever vaccine and other parenteral or nasal live vaccines should be separated by at least 30 days if possible. Either interval is acceptable.