It's possible that the North Koreans who fled the country coated the women's hands with protective chemicals first. An antidote, atropine, can be administered after exposure, but there is also the question of how everyone else in the crowded airport avoided exposure.
The most logical answer so far comes from Vipin Narang at the Massachusetts Institute of Technology.
He has suggested the attack required two people for one good reason — with the VX, he says, used in a "binary form."
Narang says one of the accused may have had a sulphur-containing liquid on her hands. The other then perhaps wielded a "complex but nontoxic compound called QL."
Combined, they create VX.
Makes sense to this non-chemist.