Harmful Tax Prevention Act This bill amends the Patient Protection and Affordable Care Act to allow a health insurer to reduce its 2018 annual fee by the amount of premium rebates provided to enrollees under this bill. Premium rebates must be equal to the lesser of 2% of the net premiums for each individual or the premiums paid by an individual. For a Medicaid managed care organization, the 2018 annual fee shall be reduced by 2% of the net premiums.