How effective is emla (lidocaine and prilocaine) cream for injection pain?

Not effective. To be effective, EMLA (lidocaine and prilocaine) should remain in contact with the skin under an occlusive dressing for at least one hour. Use local anesthetic (e.g. Lidocaine, Mepivacaine, Septocaine) for local infiltration. Talk to your health provider for side effects and allergies. Good luck.
Not much. Despite the ads from this drug maker and salespersons, this drug is not very effective and nearly worthless except as a placebo. When you think about it, that only makes sense. The skin is a barrier to water, oil, bacteria, air, dirt, and more. Why would good skin let this drug through easily? In practice, it makes injections worse for some by focusing their attention on the injection site.
Effective. if used properly, takes time, and won't help with deeper structures if involved.