Tuesday, November 10, 2009

Flu vaccine costs and benefits

I was surprised to find out that getting a seasonal flu shot isn't the slam-dunk, you're-dumb-if-you-don't-do-it decision that I assumed it was.

I think I was confounding what I know about childhood vaccines (which are a don't-be-an-idiot-and-just-get-them kinda thing) with the flu vaccine. There are good discussions on the Overcoming Bias and Science-Based Medicine blogs, prompted by an article in Atlantic Magazine.

I'm not really concerned with the big public-policy debate over whether or not the H1N1 and/or seasonal flu vaccines save lives (or whether they save enough lives to justify the cost of a public vaccination program). For me, this was the key sentence in the Atlantic article:
Studies show that young, healthy people mount a glorious immune response to seasonal flu vaccine, and their response reduces their chances of getting the flu and may lessen the severity of symptoms if they do get it.

I HATE having the flu; I'd much rather spend 2 hours waiting in line than 2 hours of having the flu. In fact, I'd give it about a 3-to-1 ratio; I'd spend 3 hours waiting to get the flu shot to avoid 1 hour of being sick and miserable.

Now the flu vaccine isn't 100% effective. And I'm not 100% guaranteed to get it. So the cost/benefit calculations get a tiny bit tricky; here's what I figure, before factoring in my preference for waiting in the doctor's office to lying feverish in bed:

Cost of getting H1N1 : ~5 days (120 hours) of misery
Cost of getting vaccinated : 2 hours of my time
Chance of catching H1N1 : 20%
Effectiveness of vaccine: 50%
Cost/benefit ratio is : 2*(1/.5)*(1/.2) / 120 = 1 / 15

So the H1N1 vaccine is a clear winner from a cost/benefit point of view. The numbers for the normal seasonal flu are different:

Cost of getting season flu: 120 hours of misery
Cost of getting vaccinated: 1 hour
Chance of getting the seasonal flu: 2%
Effectiveness of vaccine: 20%
Cost/benefit: 1*(1/.02)*(1/.2) / 120 = 250 / 120 or about 2 / 1

Most years it is quicker to get a flu shot, and most years only about 1% of the population gets the flu (I doubled my chances because the kids pick up pretty much anything going around). But most years they have to guess about which strain of flu will be going around, and they often guess wrong.

The 2/1 cost/benefit result surprises me. If I valued an hour spent sick in bed the same as an hour waiting in a doctor's office then the seasonal flu shot probably doesn't pass the cost/benefit test. I'm going to keep getting seasonal flu shots because I'm a big baby and really don't like being sick.

I haven't factored in the fact that even if the flu shot doesn't prevent me from getting the flu, it might help me recover faster. Then again, I haven't factored in the fact that I might catch a cold or another virus from somebody waiting in line with me to get a flu shot...

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