Transmission, Pathogenicity, Virulence and Vaccines

[indigo girl]

Part I

CDC's Advisory Committee on Immunization Practices (ACIP) recently rolled out their 2009 Recommendations. It's for seasonal flu, for which a vaccine exists, not for swine flu, for which there is (as yet) no vaccine. There is a lot to say on the subject of vaccines (see what we've said over the years under the vaccine category), but this seems like a good time to review some basic terminology, including what is meant by vaccine efficacy or effectiveness and how it is measured or estimated. There's a lot to say, so we'll split this into two posts, and in this one we'll go over some terms and concepts we'll need later and that are also used in thinking about infectious disease. We've done this before, of course. But it's like the Henny Youngman joke. Man goes to the doctor complaining of pain in his shoulder. "Did you ever have it before?" the doctor asks? "Yes," says the patient. Doctor: "Well you have it again." Once again, we talk about transmissibility, pathogenicity and virulence.

Read on »

http://scienceblogs.com/effectmeasure/2009/07/transmission_pathogenicity_vir.php

The Editors of Effect Measure are senior public health scientists and practitioners. Paul Revere was a member of the first local Board of Health in the United States (Boston, 1799). The Editors sign their posts "Revere" to recognize the public service of a professional forerunner better known for other things.

[indigo girl]

Part II

CDC wants us to get vaccinated for flu every year. Always for seasonal flu, and this year, if there is a vaccine available, for swine flu. They want us to get vaccinated because they think the vaccine works and they want to prevent people from getting influenza, always a dangerous and unpredictable disease, even if most of us usually escape with just a flesh wound. CDC backs up its recommendations by a quite a few scientific studies demonstrating the vaccine is effective, citing figures that the vaccine is 58% effective or 91% or effective or some other number, depending on what group is being talked about. This post is not about contradicting CDC, since I mostly agree that flu vaccination programs are sound public health. It is about clarifying some things that are glossed over when CDC talks about vaccine efficacy and explaining why this is not such an easy thing to figure out.

Read on »

http://scienceblogs.com/effectmeasure/2009/07/transmission_pathogenicity_vir_1.php

The Editors of Effect Measure are senior public health scientists and practitioners. Paul Revere was a member of the first local Board of Health in the United States (Boston, 1799). The Editors sign their posts "Revere" to recognize the public service of a professional forerunner better known for other things.

[hikernurse]

Indigo, thanks for keeping us updated on the flu. I've appreciated reading your posts about it; you're doing us all a great service