Open enrollment on the Affordable Care Act (ACA) federal insurance exchange,, opens today with millions of people facing huge premium increases along with a loss of options.

In Arizona, for instance, consumers will have the choice of just one insurer in all but a single county, and in Southwest Florida residents also have just one option, Florida Blue. Meanwhile, premiums in Arizona are rising a whopping 112 percent, while nationwide the increase averages 25 percent.

Not to worry, say spokespersons for the Obama administration. Federal subsidies will cover the increases for most folk.

“This year, the vast majority of consumers will qualify for tax credits that help keep coverage affordable, and it’s easier than ever to shop around and compare options,” Health and Human Services Secretary Sylvia M. Burwell said in a statement.

Premium increases are largely due to an enrollment flood of older and sicker consumers, many with diabetes, coupled with a dearth of younger and healthier enrollees, who would just as soon pay the tax penalty as buy health insurance they don’t think they need. An ACA program called risk corridors has also failed to raise enough revenue to cover the insurers’ losses.

As a result, insurance giants Aetna, UnitedHealthcare and Blue Cross Blue Shield have abandoned unsustainable markets and raised premiums in others. Other insurers are adjusting accordingly.

Because of the resulting cancelation of policies in counties being abandoned, ACA administrators have extended the enrollment period for those with canceled policies until Dec. 31 for policies kicking in on Jan. 1, 2017. The deadline for start-of-year coverage for everyone else is Dec. 15.