Swine Flu vaccination and consent — you read it here first

Image: Mark Diamond

Image: Mark Diamond

The Age newspaper this morning is carrying a story [1] on the new Panvax ® H1N1 influenza vaccine manufactured by CSL Ltd. About two thirds of the way through the article, there is a paragraph reading

“Concerns include the development of a consent form that each recipient must sign. There is not yet enough data from trials of the drug to inform patients of the risks involved.”

It’s five days since I first wrote about the difficulties of patient consent in relation to the new vaccine so it’s pleasing to see that the issue will now get a wider airing.

There are some interesting difficulties implied in the quoted comment. The suggestion is that the information in which patients would be interested would be information that relates to the trials alone. I’m not convinced that that would be true for three reasons. Briefly, they are (i) the frequency of rare events is difficult to estimate from small samples such as the samples used in the trials, (ii) the risks of cross-contamination are largely related to human factors, and we know that human performance is frequently better when it is being watched (as in the trials) than when it is not, (iii) the population who made up the trial sample is different from the population that is likely to be first-vaccinated, and (iv) some of the adverse consequences might take a long time to show up.

Estimating the frequency of rare events

For the sake of argument, assume that the probability of a vial of vaccine being contaminated is 1 per 100,000 doses administered. If there are only 400 people in the trials then the chance that there will be an actual contamination is relatively small, and the chance of the contamination being detected is even smaller. Once a vial is contaminated and the contamination is not detected, then given a 10 dose vial and assuming a 100 percent infection rate from contaminated needles, one can expect 4–5 people to become infected. So cross-contamination might be rare, but given an occurrence the infections then cluster.

Patient differences

The people that the government is proposing to vaccinate are an unusual subset of the whole population. They include, at a higher rate than average, the people whose health or resistance has in some way already been compromised and so, I think, are more likely than the average person to have an infection of some sort. As a consequence, by estimating by the probability of cross-infection from the trial data, one is likely to under-estimate the actual risk in the mass vaccination program.

Human performance

If you are a health practitioner and you know that you are part of a study on the risks of using multi-dose vials, then you are likely to perform better than if you were just giving vaccinations without being studied. The likely change in your behaviour, which is known as the Hawthorne effect, will result in the risk of cross-infection being underestimated.

Delayed consequences

If the cross-infection that you get is Creutzfeldt–Jakob disease (CJD), then your infection is unlikely to show up for a long time and will also result in the risks being underestimated. Nonetheless, harking back to the Rogers v. Whitaker decision that I referred to in the earlier posting, I expect that patients would consider the CJD risk to be “material” even if it is very very very very small.

[1] Miller, N. (2009). Doctors urge delay on vaccine. The Age. 29 August 2009. http://www.theage.com.au/national/doctors-urge-delay-on-vaccine-20090828-f2k6.html

Contributors: Mark R. Diamond