Mother:

I am debating whether Caitlin should get the H1N1 shot tomorrow. I am not inclined to give her the normal flu shot, mostly because I prioritize vaccines for measles and other things that seem more life-threatening, but H1N1 is scarier. She's 17 months old. What do you think? (names changed)

Rob:

This vaccine, like nearly every effective treatment ever made, has dangers. The relevant question is not whether danger exists, but whether likely benefits outweigh likely harms.

In prior years the flu vaccine's ability to reduce death was much greater than its likelihood of causing any side effect more serious than a sore arm.

In otherwise healthy kids Caitlin's age who got flu last spring, the probabilty of death from H1N1 "swine" flu was between .001 and .0001; the probability of serious side effects in flu vaccines historically ranges around .00001-.000001. The incidence of H1N1 flu this upcoming fall is unknown, and is important in this analysis.

Studies on the new vaccine could not determine the risk of serious side effects because no serious side effects were reported so far in over 39,000 people who have received it. These studies found that the vaccine is good at preventing swine flu.

Between now and when you'll have to decide what to do for Caitlin, it's unlikely that we will obtain new, useful information to help guide this decision.

Will this vaccine be different from prior flu vaccines?

It's probably just like every other flu shot. It was made using the same process to make the standard seasonal flu vaccine.

There could always be a new, common, and devastating side effect with this vaccine--just because something has never happened before doesn't make it impossible (e. . Popper's black swan, also the 2008 housing crisis).

You said the process for making H1N1 vaccine was the same as for prior flu vaccines. Why then are there all these worries about the safety of it?

If there is any scientific basis for the worry, I am not aware of it. Popular culture concerns over health issues follow a rhythm and a logic that I do not understand. Did you read the New Yorker article about the 1920's Parrot Fever that spread in the US? It probably addresses your question better than I can.

Timing. It takes a while between when we identify a pathogenic flu strain and when we can create a vaccine, establish saftey/efficacy, and produce hundreds of millions of doses. If the swine flu outbreak last winter had begun a few months sooner, then there would have been enough time to incorporate the swine flu vaccine into the seasonal vaccine this year.



For other flu shots, last year's seasonal flu shot for example, do they test the safety of that specific flu shot before distributing it for widespread public use?

Yes. Same process.

Do you think that if we waited another month we'd have any more info - if the 39,000 people were to become 100,000, for example, as a result of widescale vaccination campaigns?

Sure, but this also increases Caitlin's risk of catching swine flu during the wait.

One more - what is the likelihood of side effects occurring a while after the vaccine - i.e. for the 39,000 people to be fine now but develop a problem sometime in the near future? How long does Guillain-Barre take to manifest?

Another good question.

And a tricky one. Some scientists argue that the flu vaccine does not cause Guillain-Barre syndrome (GBS), and that the extra GBS cases we saw during the 1976 round of flu vaccination were coincidental. It's usually challenging to establish causality in anything that's occurring in 1 in 100,000 people. I don't have an opinion here.

How much time passes between vaccine administration and GBS? I don't know the answer. I suspect the data set we have on this is so tiny that you can't figure it out--which is to say, I'm guessing that it is not knowable. For what it's worth, I've never seen a case of GBS in my 10 years of doing medicine. Here's more info on the history of GBS and the flu vaccine:

http://www.nytimes.com/2009/05/09/health/09vaccine.html

What's your personal opinion?

I'm getting my H1N1 shot in the next few weeks; got the seasonal shot 3 weeks ago. "Doctors aim to prevent death. The long-term death rate is 100%. Therefore, all doctors are failures."