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...


  1. The mask worries me. There are unpublished data showing that masked HCWs touch their face more, which puts them at higher risk of auto inoculation with respiratory pathogens. And perhaps the distraction of the mask could lead to errors. The other mask issue that makes no sense to me is requiring unvaccinated HCWs to wear a mask--if you believe the mask is effective, and knowing that the vaccine is not that great (60% effective in a good year), shouldn't everyone (vaccinated and unvaccinated) wear masks? This logic exposes the true reason behind the mask--it's punitive and coercive. I will never understand why everyone jumped on the vaccine mandate. I think it's mostly a public relations ploy.

  2. So you don't like "chin warmers" Mike? Masking as a punitive move to shame the unvaccinated seems to make sense only if influenza vaccine is 80-100% effective.

    And if masks are at all effective, what if your prevailing respiratory virus causing ILI is rhinovirus, Human Metapneumovirus, or adenovirus? Who are you protecting with the masks? Our information from viral panels done during respiratory clusters or outbreaks have shown that we have not had a single pure outbreak (one viral type) since 2012. The prevailing viruses have included hMPV, RSV, Influenza A and B, adenovirus and most recently rhinovirus which caused clusters of illness with pneumonia and ILI. We have also had patients have more than one virus at the same time, some are spread by droplet and some by contact. Hence we have combined Contact/Droplet precautions for respiratory or gastrointestinal illness

    We close cohorts with respiratory or GI clusters, and mask every employee or visitor in our LTCF for anyone entering that unit, We also cohort staff, suspend group activities, have in-room therapy as opposed to having patients move off the unit to common therapy rooms, and enhance environmental cleaning/disinfecting. The approach seems to be an efficacious for us to control outbreaks and spread of disease to other units.

    We do not mandate influenza vaccine, but our employee rates have exceeded 80% for over 5 years. However,recently, our most recent outbreaks have seemed to come from family and visitors. We are pretty militant about sending ill employees home. It is a complex issue.

    1. Thanks for sharing your thoughts. I always learn a lot from your comments.


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