According to figures released by HHS, only one quarter of the 2 million Obamacare enrollees who signed up through December are young adults - 18-34. On the other side of the coin, fully one half are 45-64.

The White House says that 25% enrollment of young invincible is enough to prevent the dreaded "death spiral" for the program, where older, sicker enrollees far outnumber the younger healthy ones, thus leading to skyrocketing insurace premiums.

But there are no figures available that show how many enrollees have actually paid their first month's premium, nor is there any breakdown of how many in the 18-34 age group are healthy and how many are sick.

Wahington Post:

The figures mean that the proportion of young adults is lagging behind what both government and outside health policy analysts have said will be required for the exchanges to remain stable. Analyses have concluded that, to prevent health plans' premiums from rising and some insurers from potentially dropping out, roughly two in five Americans in the plans should be young adults.

In releasing the report, Obama administration officials were upbeat. The latest enrollment figures are "solid, solid news for us," a senior administration official told reporters at a White House briefing. The officials predicted that the health plans would attract more young adults during the second half of the open-enrollment period for this year, which continues through March.

Still, the report's numbers increase the significance of outreach efforts designed to persuade young people to sign up. Whether sufficient numbers of young people will do so, despite the law's requirement that most Americans have coverage or face a financial penalty, has been an uncertainty hovering over the law.

Administration officials said Monday that their plans to intensify promotional efforts aimed at young adults will focus on two dozen communities in states such as Texas that rely on the federal marketplace and have especially large uninsured populations.

Health policy specialists and industry officials said it is too early to know whether the enrollment patterns will shift in the next few months, although Republicans wielded the new figures as their latest weapon to condemn the federal health-care law.

"Youth enrollment has been a bust so far," said Brendan Buck, spokesman for House Speaker John A. Boehner (R-Ohio).

Larry Levitt, senior vice president at the Kaiser Family Foundation, said the proportion of young people "is lower than would be ideal." Still, he said, the data were "encouraging," given that people have another 2¹ / ₂ months to enroll and that the federal online system, HealthCare.gov, had defects that prevented many people from signing up for much of the fall.

In a study last month, the foundation concluded that 40 percent of the people who could benefit from the new insurance marketplaces are 18 to 34 years old - and therefore, the pool of people who join the plans should match that proportion. The study also predicted that if the proportion of young people remains roughly as low as it is now, it could reduce health plans' income from premiums in ways that, while not huge, could nevertheless cut their typical profits roughly by half.

One indutry expert estimated that only 50% of enrollees had paid their first month's premium. But the insurance companies have extended their payment deadlines - many until the end of January - to accommodate those who signed up at the last minuite.

Given that the mix of sick versus healthy enrollees is "more adverse than previously expected," according to one Humana official, the chances that the Obamacare bailout provisions will be triggered are very good. Republicans should jump on this issue with both feet and force the president and Democrats to defend bailing out the insurance companies.

Let the Democrats run on that in November.