Controversial “vaccinate or mask” policies that force nurses to get a flu shot, or wear a surgical face mask for the entire flu season, are based on flimsy science that lacks credibility, according to new analysis.

The and published on the peer-reviewed open access scientific journal PLOS One on Friday, casts serious doubts on whether Canadian health care workers should have to get the flu shot to work in hospitals, clinics and long-term care facilities.

No province enforces mandatory flu shots for health care workers. But a “vaccinate or mask” (VOM) policy has been in place in B.C. since 2012. Some hospitals in Ontario and Nova Scotia have adopted similar policies, but they are not required province-wide. Alberta and Saskatchewan briefly introduced and later retracted their own VOM policies.

Evidence in support of vaccinating nurses comes from four studies conducted in long-term care facilities. In their new analysis, researchers took a closer look at the four studies to determine if patients actually benefitted from health care workers getting the flu shot.

Researchers found that all four studies reported “implausibly high benefits to patients” that defied calculations. Even with “optimistic assumptions,” the reduction in patient deaths exceeded expected values tenfold and were “impossible” to attribute to the flu shot.

To give an idea of how implausible the results were, researchers pointed out that one study suggested that one patient death could be prevented for every eight health care workers given the flu shot.

If this conclusion were true, researchers say, then vaccinating all hospital staff in the Canada and the U.S. would prevent more deaths across those populations than occurred in both countries during the 1918 influenza pandemic, which was one of the deadliest disasters in recorded human history.

“That conclusion is utterly impossible,” the researchers write in the summary. “For it to be true, (the) influenza vaccine would have to be a truly miraculous intervention for the sheer scale of its indirect patient benefits.”

Researchers go on to suggest that fears health care workers are putting patients at “great peril” by not getting the flu shot are “exaggerated.”

The report cautions that the findings don’t mean that the flu shot is useless, but rather that the necessary scientific proof behind VOM policies is lacking.

“This does not refute approaches to support voluntary vaccination or more broadly protective practices, such as staying home or masking when acutely ill.”