From the beginning, I have argued on this blog that SHEA's position was misguided for a number of reasons that I won't rehash in this post (see here, here, and here). Moreover, the Cochrane group evaluated the same four papers on which SHEA based its recommendation and determined there was no conclusive evidence that vaccinating HCWs was effective in reducing influenza in patients. But SHEA didn't back down. Another systematic review by another group came to the same conclusion. But SHEA didn't back down. CDC significantly downgraded the effectiveness of influenza vaccination to worse than placebo in some years. But SHEA didn't back down. And there's even a lack of evidence that influenza vaccine of healthcare workers reduces influenza in healthcare workers.
Now comes a 21-page paper (free full text here) in PLoS One by a group of Canadian epidemiologists that decimates those four nursing home studies. And all I can say is: SHEA better back down.
According to these investigators, all four studies violate the principle of dilution by reporting greater percentage reductions with less specific outcomes (i.e., the studies report percentage reductions in all-cause mortality > influenza-like illness (ILI) > laboratory-confirmed influenza). The principle of dilution requires that vaccine efficacy must be lower when non-targeted events (non-flu illnesses) are included in the study outcome than when only the target (confirmed influenza) contributes. The authors give the simple analogy of using an item-specific coupon at the grocery store--the percentage reduction in price on that item will always be much greater than the percentage reduction on your entire purchase that includes multiple other items. It's an irrefutable law of mathematics.
They also note several sources of bias. Depending on the study, there were differences in mortality between the control and intervention groups accrued before influenza arrived in the community, and there were issues with the definition of ILI. Estimates of numbers need to vaccinate were so flawed (off by as much as 4,000-fold) that if extrapolated to all healthcare workers in the US, more deaths would be averted than occurred in the 1918 influenza pandemic.
Here's the bottom line per the authors: Each of the four cluster RCTs used to champion compulsory HCW influenza vaccination policies reports benefits that are mathematically impossible under any reasonable hypothesis of indirect vaccine effect. It's hard to imagine a stronger conclusion.
If you don't read the entire paper, please read the discussion. Here's the concluding paragraph:
Through this detailed critique and quantification of the evidence we conclude that policies of enforced influenza vaccination of HCWs to reduce patient risk lack a sound empirical basis. In that context, an intuitive sense that there may be some evidence in support of some patient benefit is insufficient scientific basis to ethically override individual HCW rights. While HCWs have an ethical and professional duty not to place their patients at increased risk, so also have advocates for compulsory vaccination a duty to ensure that the evidence they cite is valid and reliable, particularly in the absence of good scientific estimates of patient impact. The diversion of resources from more evidence-based efforts and other important but less tangible costs related to loss of trust and credibility also need to be considered, including the implications for other immunization programs and workplace policies. Although current data are inadequate to support enforced HCW influenza vaccination, they do not refute approaches to support voluntary vaccination or other more broadly protective practices such as staying home or masking when acutely ill.
And if that's not enough, there's a commentary in the same journal, responding to the Canadian study written by the lead author of one of the nursing home studies. He defends his study, but importantly he states that the findings should not be extrapolated beyond the nursing home setting.
As I see it, unless SHEA cites alternative facts, it has three choices: change its position to recommending (not mandating) annual influenza vaccine for healthcare workers, articulate a damn good reason to support its current policy despite the evidence (hard to imagine what that would be), or simply retire the guideline (as it has quietly done for the 2003 highly controversial MRSA/VRE search and destroy recommendation). Given the assault on science that we are likely to see over the next four years in the US, SHEA must lead by ensuring that all of its recommendations are solidly based in evidence and that expectations for compliance with interventions correlate with the strength of the evidence. Just as we must defend vaccines from false claims of adverse effects, we must also truthfully acknowledge their limitations and shape our policy on science not opinion.
