Tuesday, September 29, 2009

The Flu Shot Controversy

A large Canadian study has found that people who got the seasonal flu shot last year were more likely to get H1N1 this spring than people who didn't get the shot. The report is not yet peer-reviewed, but reports of the report are causing Canadian officials to rethink their flu shot policy. However, the researchers should have expected that certain biases would provide this result, without implying that the seasonal flu shot somehow causes H1N1:

1. People who get the seasonal flu shot are more likely to get flu
Some people never get the flu, because of natural immunity or because they don't spend time in close proximity to infected people. These people are much less likely to get flu shots.

Conversely, some people are much more prone to getting sick, due to poor health, close proximity to infected people, or whatever. These people are much more likely to get the flu shot.

So in the sample group, you would expect more people who got the flu shot to get this new strain of flu. That doesn't mean that the flu shot caused the flu.

2. People who get the flu shot are more likely to be diagnosed with H1N1
This past spring, most people who got sick with H1N1 got mild cases. Most were probably not even diagnosed. The people who were diagnosed with H1N1 are probably those people who go to their doctor more often. People who go to their doctors more often are more likely to get the flu shot. Therefore, of the people who got H1N1, those who are diagnosed are more likely to have had the flu shot.
Correlation does not imply causation.

This sort of research can suggest lines of laboratory research, but it means little without the research. And yes, that applies to all the other statistical health studies we read about in the newspaper.

Unfortunately, immunizations have become the hot topic of people who are paranoid about the medical profession: people who hate doctors, or mistrust science in general, or think BigPharma is manipulating health issues to boost profits.

As for myself, for most of my life I got the flu every year, usually getting sick as a dog and missing a full week of work or more. Every year since 1997 I've had a flu shot and in that time I haven't had the flu. Ontario has now decided to delay seasonal flu shots till after the H1N1 shots, and that increases my likelihood of getting the flu. So I feel I have a personal stake in this. For those who don't want to get flu shots - fine; as long as they stay away from other people when they get sick, they can do what they like. But as a public policy, flu shots work, and shouldn't be delayed until the middle of flu season on such a questionable and preliminary study.



The Rat said...

Wouldn't it be nice if you could make a decision like that for yourself? Doesn't it feel strange that a decision that directly affects your health is being made by a distant bureaucrat? Ahhh, the joys of socialism and socialized medicine. You are now reaping just a small taste of what you have sown.

Yappa said...

The Rat -

Ha! Ha! Ha!

The only difference in flu shot policies between Canada and the US is that here the shots are free.
Bureaucrats make the call in both the US and Canada.

Lizt. said...

I asked my doctor yesterday if getting the Seasonal Flu shot, lowers your immunity , so you get the H1N1 flu..he said no your immunity goes up with the Sesonal one. The American doctors say the same thing.

Yappa said...

Hi Lizt,

I have read the same thing. They believe that people who get the flu shot every year develop a stronger and broader immunity to flu. That makes sense.

Anonymous said...

This study included thousands of people. The risk of H1N1 was double in those that had been vaccinated, that's a 100% increase. Also 98-99%of the flu that is showing up thisyear is H1N1. This is the seasonal flu this year, not the strains in the "flu" shot. These scientists are aware or correlation vs causation. 100% increase in risk is not something to be taken lightly. Ifyou are prone to getting the flu, you are much better off with the H1N1 vaccination than one for strains that aren't circulating this year.

Bert said...

Wow Yappa. A post I can agree with ;-).

I'm a diabetic and get the flu shot every year. So far, all is good. A few minor sniffles, but nothing major.

Anonymous said...

I have just read an article in the Vancouver Sun regarding a young woman that developed a dibilitating syndrome called Gullaine-Barr after having a flu shot. She was paralyzed after just 2-3 days and had to relearn walking etc. and she still has not fully recovered. The article states that your chances of having this type of reaction increase 45% with a flu shot. My daughter is diabetic and had a flu shot 2 winters ago and was sicker that year than she has been in many years. What is the correct decision for a family regarding this important health issue? Who do you believe? The government, general practitioners or alternative health providers?