The Department of Justice is digging in its heels against UnitedHealth Group, alleging in a second lawsuit the health insurance giant has knowingly scammed the government by inflating the medical codes of its Medicare Advantage members.

But UnitedHealth is not the only Medicare Advantage insurer under the federal microscope — it's just the largest, covering about one-fourth of all people in the program. The DOJ also is investigating Humana, Centene and other insurers for their coding practices.

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Data: Centers for Medicare and Medicaid Services; Chart: Lazaro Gamio / Axios

The big picture: Medicare Advantage is the private version of Medicare that has more limited networks of doctors and hospitals but cheaper premiums, and it is heavily consolidated. The four biggest companies — Aetna, Humana, Kaiser Permanente and UnitedHealth Group — control 56% of the market. Any scrutiny or changes in payment policies will affect those insurers most.

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Updated 2 hours ago - Politics & Policy

Coronavirus dashboard

Illustration: Sarah Grillo/Axios

  1. Global: Total confirmed cases as of 10 a.m. ET: 19,412,292 — Total deaths: 722,066 — Total recoveries — 11,773,112Map.
  2. U.S.: Total confirmed cases as of 10 a.m. ET: 4,945,795 — Total deaths: 161,456 — Total recoveries: 1,623,870 — Total tests: 60,415,558Map.
  3. Politics: Trump says he's prepared to sign executive orders on coronavirus aid.
  4. Public health: Fauci says chances are "not great" that COVID-19 vaccine will be 98% effective
  5. Science: Indoor air is the next coronavirus frontline.
  6. World: Africa records over 1 million coronavirus cases — Gates Foundation puts $150 million behind coronavirus vaccine production.
2 hours ago - Health

Indoor air is the next coronavirus frontline

Illustration: Eniola Odetunde/Axios

A growing body of research has made it clear that airborne transmission of the coronavirus is possible.

Why it matters: That fact means indoor spaces can become hot spots. Those spaces also happen to be where most business and schooling takes place, so any hope for a return to normality will require better ways of filtering indoor air.

The silver linings of online school

Illustration: Annelise Capossela/Axios

Online learning can be frustrating for students, teachers and parents, but some methods are working.

The big picture: Just as companies are using this era of telework to try new things, some principals, teachers and education startups are treating remote learning as a period of experimentation, too.