Millions of Americans lose their health insurance plans every month, by leaving the job through which they got that coverage, Axios' Bob Herman reports.

Why it matters: Critics and skeptics of "Medicare for All" worry about eliminating people's existing coverage because most people are relatively satisfied with their employer-based plans.

• But millions of workers and their families already switch or lose their insurance from their jobs.

By the numbers: More than 66 million Americans voluntarily quit their jobs, were laid off or otherwise separated from their employers in 2018, and that high turnover rate has continued into 2019, according to data from the Bureau of Labor Statistics.

Details: The BLS data does not measure whether separated jobs offered health insurance.

• However, close to half of all private employers provide coverage to their workers, and more than 90% of companies with at least 100 employees offer health benefits.
• It's therefore reasonable to estimate that at least 2 million workers and their families lose or transfer to new commercial health plans every month.

The bottom line: Behavioral economics teaches that people don't like to lose what they have, a concept known as "loss aversion."

• But U.S. workers churn through a dozen jobs in their lifetimes, on average, so people rarely keep their same private health plan over time.

Go deeper:

• How Medicare for All could impact employers
• The unique problem with U.S. health care
• How your health care would change under Medicare for All

Primary care only accounted for between 2.1% and 4.9% of total Medicare spending in 2015, depending on how primary care is defined, according to a new RAND study published in JAMA Internal Medicine.

• Greater focus on primary care is associated with high quality health care and lower costs.
• While there's no consensus on what percentage of health care spending should go toward primary care, the RAND estimates are lower than estimates of what other countries spend.

Spending on primary care was lower among beneficiaries who were older, black, Native American, dually eligible for Medicare and Medicaid, and who had chronic conditions. Rates also varied by state.

Why it matters: Primary care is a lot cheaper than, say, surgery for a condition that has gotten worse while untreated. We may not know the magic percentage of spending that should go toward primary care, but it's a good thing to consider when we talk about lowering costs.

Measles cases in the U.S. jumped last week, with 90 new confirmed cases, the Centers for Disease Control and Prevention announced Monday.

• The extremely contagious virus, for which there is a safe and effective vaccine, shows no signs of slowing despite efforts by public health authorities to combat the spread of misinformation with strong measures, Axios' Eileen Drage O'Reilly reports.

By the numbers: This week, the CDC reports 555 confirmed cases of measles in 20 states so far in 2019. The previous week showed 465 cases in 19 states.

• This is the second-greatest number of cases reported in the U.S. since measles was considered eliminated in 2000, and it's only mid-April.

The Wall Street Journal reports there's growing evidence that the virus may cause a longer-term risk of dampening people's immune systems from responding to other diseases for 2–5 years after measles.

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You read that headline correctly. The Department of Homeland Security has considered designating fentanyl a weapon of mass destruction in certain situations, Task & Purpose scooped yesterday.

• "Fentanyl's high toxicity and increasing availability are attractive to threat actors seeking nonconventional materials for a chemical weapons attack," James McDonnell, a senior DHS official, wrote in a memo obtained by Task & Purpose.

Between the lines: Yes, fentanyl — which is much more potent than prescription opioids — can be deadly and, yes, it's a huge problem.

• But the public discussion over the opioid epidemic has not to date been about opioids becoming weapons of mass destruction. And yet the administration has been discussing this possibility for years, according to the memo.

Teaching and rural hospitals had lower penalties in 2019 than in 2018 under the Centers for Medicare and Medicaid Services' readmissions reduction program, Modern Healthcare reports.

• This was the intended consequence of changes made to the program to take into account the patient mix in these hospitals. The hospitals — particularly safety net hospitals — had said they were unfairly penalized.
• The changes, which were made through the 21st Century Cures Act, sorted hospitals into 5 categories based on the proportion of their patients that were dually eligible for Medicare and Medicaid.

Details: According to a JAMA Internal Medicine report, 44.1% of teaching hospitals and 43.7% of rural hospitals had a lower penalty this year than last year.