Holy shit! Remember the problem with East Asia's unbalanced male-to-female ratio? Some bright new spark has done some pretty heavy-grade data mining to make the argument that at least half of the imbalance is historically due to patterns of Hepatitis B infection, which apparently has a significant effect on how many girl babies are brought to term on infected mothers.
I don't know that it changes the immediate demographics - the damage is done, and they aren't going to bring back lost women to generations already born - but widespread Hepatitis B vaccination may correct the situation in generations yet to be born. On the other hand, as is pointed out in the above article, this only accounts for half of the effect, and it's possible that the horrible social and cultural practices and attitudes probably responsible for the balance of the gender deficit will just kick into overdrive, and ramp up the infanticide machine to eliminate the potential women restored by the hypothetical removal of the Hepatitis B factor.