You might need to wash them with muriatic acid solution.
The manufacturer might have a suggestion or tow.

"I used the plate compactor to vibrate sand into the cracks"

The action of the plate and sand might have "sanded" the surface of the blocks. Try sealant, in an inconspicuous area.

yes a sealer would more then likely fix this problem try techni seal or surebond you should be able to buy them from your pavestone distrubutor. Do Not use moratic acid on pavers it will fade them or could make the problem worse.

Thanks for the suggestions. I did not want to use muratic acid as I have landscaped around the patio and don't want runoff to kill hte plants. when it stops efflorescence generation, I'll try the sealer. Our moist conditions in the Pacific NW seem to keep the efflorescence coming on.
Ed

i was considering dry-laid concrete pavers for a walkway in a very shading area and was concerned about efflorescence ... is there a way to avoid this in a shady area -

You probably compacted the surrounding clay / soil into the pours of the pavestones s.

If a broom and water won't penetrate the pours to remove the grime then we use a light muriatic acid wash.

If done correctly and at the right percentage it does not change the color of the pavestones and if run off is highly diluted and controlled you will not lose any plant

There are also a variety of stone cleaners out there that are effective yet expensive in comparison to the acid.

Prosoco makes a very effective line of masonry cleaners, degreasers and sealers.

I particularly am very pleased with their STMP sealer which in our test slabs has kept red wine, hamburger and straight poured on olive oil from staining our hand cut and flamed bluestone countertops for an outdoor kitchen counter top.
Pricey stuff, at $ 100 for a gallon, but the most effective product we have found to date.