Influenza Vaccine Mandate Math
Last week, I described five steps individual hospitals, systems and society should take when implementing compulsory influenza vaccination of healthcare workers. One component of many influenza vaccine policies is mandatory surgical masks for healthcare workers who refuse or otherwise cannot receive the vaccine. Does masking unvaccinated healthcare workers even make sense? Or rather, who is more likely to spread influenza in hospitals - an unmasked, vaccinated healthcare worker or an unvaccinated, masked healthcare worker? Let's look at the numbers.
Let's assume influenza vaccine is 50% effective. In 2014-15, overall effectiveness was 19% while in 2012-13 and 2013-14 it was 49% and 51%, respectively. I'll give the vaccine a mulligan last year since during the prior decade, vaccines were far more effective. Let's further assume with vaccine mandates, 90% of healthcare workers receive the vaccine and 10% do not.
If 90% receive a vaccine that is 50% effective, we will have 45% of healthcare workers in our hospital protected and 45% unprotected. The tricky thing is that we won't know who is protected or unprotected. And what if the 45% vaccinated but non-immune healthcare workers assume they are immune and work while sick? You can imagine them saying - "I'm sick, but it's not influenza because I was vaccinated, so I'll do my ICU shift." Any mandatory vaccination policy should consider that scenario or it's possible that the mandate could make hospitals less safe. But what of the 10% required to wear masks? I suspect they'd be more likely to stay home if sick, but even if they don't they'll be wearing a mask!
Finally, if I had a choice between being cared for by a vaccinated, unmasked healthcare worker or a masked, unvaccinated healthcare worker, I'd chose the mask. That is, until we implement influenza prevention bundles that focus on presenteeism.
Note: Mike wrote a fantastic quantitative post (in 2010!!) comparing a vaccine mandate to a presenteeism reduction policy. His conclusion: "Reducing presenteeism by 1 percentage point (from 70% to 69%) would have the same impact as increasing vaccination from 70% to 98%." It's too bad not many read the blog back in 2010...