The top US health department plans to require placebo testing for all vaccines in an effort to offer "straightforward" public health information, but experts say such testing could limit availability and raise ethical concerns.

The report, released Tuesday, confirmed the classical pianist died of hantavirus pulmonary syndrome (HPS) in mid-February at age 65. Michael Bolton has glioblastoma, a treatment-resistant and incurable cancer. The revelation comes 16 months after he had emergency surgery to remove a brain tumor.

The Department of Health and Human Services says it will require new vaccines to be tested against a placebo, which could complicate and delay Food and Drug Administration approval of many vaccines.