Influenza vaccination, herd immunity, and the Tragedy of the Commons

Dec 24, JDN 2458112

Usually around this time of year I do a sort of “Christmas special” blog post, something about holidays or gifts. But this year I have a rather different seasonal idea in mind. It’s not just the holiday season; it’s also flu season.

Each year, influenza kills over 56,000 people in the US, and between 300,000 and 600,000 people worldwide, mostly in the winter months. And yet, in any given year, only about 40% of adults and 60% of children get the flu vaccine.

The reason for this should be obvious to any student of economics: It’s a Tragedy of the Commons. If enough people got vaccinated that we attained reliable herd immunity (which would take about 90%), then almost nobody would get influenza, and the death rate would plummet. But for any given individual, the vaccine is actually not all that effective. Your risk of getting the flu only drops by about half if you receive the vaccine. The effectiveness is particularly low among the elderly, who are also at the highest risk for serious complications due to influenza.

Thus, for any given individual, the incentive to get vaccinated isn’t all that strong, even though society as a whole would be much better off if we all got vaccinated. Your probability of suffering serious complications from influenza is quite low, and wouldn’t be reduced all that much if you got the vaccine; so even though flu vaccines aren’t that costly in terms of time, money, discomfort, and inconvenience, the cost is just high enough that a lot of us don’t bother to get the shot each year.

On an individual level, my advice is simple: Go get a flu shot. Don’t do it just for yourself; do it for everyone around you. You are protecting the most vulnerable people in our society.

But if we really want everyone to get vaccinated, we need a policy response. I can think of two policies that might work, which can be broadly called a “stick” and a “carrot”.

The “stick” approach would be to make vaccination mandatory, as it already is for many childhood vaccines. Some sort of penalty would have to be introduced, but that’s not the real challenge. The real challenge would be how to actually enforce that penalty: How do we tell who is vaccinated and who isn’t?

When schools make vaccination mandatory, they require vaccination records for admission. It would be simple enough to add annual flu vaccines to the list of required shots for high schools and colleges (though no doubt the anti-vax crowd would make a ruckus). But can you make vaccination mandatory for work? That seems like a much larger violation of civil liberties. Alternatively, we could require that people submit medical records with their tax returns to avoid a tax penalty—but the privacy violations there are quite substantial as well.

Hence, I would favor the “carrot” approach: Use government subsidies to provide a positive incentive for vaccination. Don’t simply make vaccination free; actually pay people to get vaccinated. Make the subsidy larger than the actual cost of the shots, and require that the doctors and pharmacies administering them remit the extra to the customers. Something like $20 per shot ought to do it; since the cost of the shots is also around $20, then vaccinating the full 300 million people of the United States every year would cost about $12 billion; this is less than the estimated economic cost of influenza, so it would essentially pay for itself.

$20 isn’t a lot of money for most people; but then, like I said, the time and inconvenience of a flu shot aren’t that large either. There have been moderately successful (but expensive) programs incentivizing doctors to perform vaccinations, but that’s stupid; frankly I’m amazed it worked at all. It’s patients who need incentivized. Doctors will give you a flu shot if you ask them. The problem is that most people don’t ask.

Do this, and we could potentially save tens of thousands of lives every year, for essentially zero net cost. And that sounds to me like a Christmas wish worth making.

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