Thursday, February 15, 2007

Flu Vaccine - wheeze now or sick later?

The prestigious New England Journal of Medicine just published a paper claiming to demonstrate a superiority of attenuated live flu vaccine over the conventional, dead flu vaccine for young children. About half as many kids in the attenuated vaccine group went on to contract flu (figure). USA Today and other publications trumpeted the results with headlines such as "FluMist spray protects kids better than flu shots". They downplayed the concern raised by independent scientists that the live vaccine "comes with a significant risk for medically important wheezing".
This story illustrates some of the problems with reporting such clinical trials. First, it was "sponsored" (paid for) by MedImmune, the producer of the live vaccine. Sponsors have been known to not publish disappointing results, producing a publication bias. Although we can welcome these results, the arrangement raises questions about the "spin". How should parents and pediatricians balance the decrease in disease (from 9% to 4%) with the increase in wheezing (from 3% to 6%)? Second, the description of the trial is misleading. The Methods section begins "children ... were randomly assigned receive either ... live attenuated influenza vaccine ... or inactivated vaccine in a double-blind manner" (emphasis added). This use of the term "double-blind" is nonsensical because random is completely "blind". The wording seems intended to make the reader think the trial was double-blind. Double-blind is the gold standard for trials because it reduces bias by keeping the both the doctor and patient ignorant of which treatment they are assigned. In this trial, however, the treatments could not be "blinded" because one involves a shot and the other involves sniffing the virus, treatments that are clearly distinguishable even by a patient. Finally, journals and journalists like to report positive, exciting news. These results merit a more sober discussion.
N Engl J Med. 2007 Feb 15;356(7):685-96. "Live attenuated versus inactivated influenza vaccine in infants and young children." Belshe RB, Edwards KM, Vesikari T, Black SV, Walker RE, Hultquist M, Kemble G, Connor EM

1 comment:

Anonymous said...

Horizontal transmission?
Can the live vaccine infect other people? Probably not as well as the wild-type, but even a little could provide a public health benefit in addition to protecting the individual who got the vaccine.