Flu Season: Get your flu shot.
Last year I told you to get a flu shot. This year I'm reminding you again. It's November. The start of flu season. Go get a flu shot.
To recap:
- The influenza flu shot uses a killed virus which will not give you the flu. (There's also a live nasal spray vaccination which you should not get if you're taking care of immunocompromised family members.)
- Your body will respond to the vaccine with minor symptoms that pale in comparison to the actual flu that you are trying to avoid. After my shot I felt flu-ey for about six hours. This is normal.
- You do not need health insurance or a doctor's visit to get a flu shot. For the last two years I've gotten flu shots at the walk-up counter at the Safeway pharmacy, no appointment necessary, $30. See flucliniclocator.org for the one in your area.
- The vaccine is 70-90% effective in healthy adults and 66% effective in children when the vaccine strains and the virus strains are well-matched and still 44% effective even in bad-guess years like last year because many of the protein shapes are similar.
- The big payoff is herd immunity. If everyone in your house or office gets a flu shot it's even less likely that you'll be able to pass the flu to each other. You are 1.5x less likely to give your friends the flu if you are vaccinated. See also: europeans et indians v. smallpox.
- The flu vaccine confers the most benefit to healthy adults whose immune systems are in the best shape. Avoiding the shot because children, old people, and health workers need it more is like avoiding fastening your seat belt because race car drivers need seat belts more.
Every year the CDC tries to guess which strain of influenza they're going to target. They do this by guessing whether it'll be influenza A, B, or C and which hemagglutinin ("H") and neuraminidase ("N") types this year's flu will carry. Between influenza variants A, B, and C there are 16 H proteins and 9 N proteins for a total of 432 possible types (many of which are problems for other animals but don't easily infect humans, such as H5N1). This year's guesses are A/H1N1, A/H3N2, and B/H3N2 based on this report. Even if all three guesses and all four proteins are wrong it's still not a total loss; many of the H's and N's have similar enough shapes that near-misses are still helpful. This "cross immunogenicity" is a possible reason why 45-65 year olds escaped the 1918 pandemic - because they got partial immunity to a similar flu around 1870.
Antigenic sin is something to be concerned about only if you believe that you're not going to be naturally exposed to the same disease that you're being vaccinated against (which is kinda the point of vaccination), that your body's learned response is likely to be wrong for a similar virus (which is kinda the point of our evolved immune response), and that it's better to avoid an uncommon event like a pandemic that's going to suck for everyone rather than a common event like the flu (which doesn't make a lot of sense to me). Avoiding a flu shot because it might give your system antigenic sin is like avoiding fastening your seat belt because it might trap you in your car if it's suddenly submerged.
Antigenic shift is something to be concerned about, but shift is relatively uncommon compared to drift and a vaccination is going to either help you or not affect the outcome either way. Avoiding a flu shot because it doesn't protect you from trans-species pandemics is like avoiding fastening your seat belt because it doesn't protect you from gunshot.
Economists have tried to put a number on the value of the flu shot. Depending on which country you're looking at, businesses save $53.00 per vaccinated employee in Malaysia and employees save $899.70 when you consider their operating income. Other studies put the number at $73.1-240 (Argentina) and $6.45-89.3 (Colombia). Any way you look at it, a $30 flu shot seems like a fairly good deal.
Conclusion: find a clinic, pay a few bucks if you don't have insurance, and go get vaccinated especially if you have or care for children or old people, live in my house, or work with me.
(This post has been peer-reviewed by chemicalpilate, who knows things.)
Update: This episode of Quackcast covers what I just said, but he is smarter.
Update 2: I got sick anyway.