Pneumonia vaccine ineffective?
“Pneumonia vaccine ineffective against repeat infections: study” screams the headline. The article goes on to clarify that a study just published seems to suggest that the pneumococcal vaccines in use in Canada do not seem to perform any better than no vaccine. How is that possible? Well, so far as I can tell, it isn’t, and this seems to be another case of dubious reporting by the journalists, and careless conclusions by paper authors.
I could not get my hands on a copy of the full published study the article refers to, although I will probably be able to in the near future. In the mean time, all I can go on is the abstract which can be found at PubMed or at Chicago Journals. Let us examine exactly what this study seems to suggest, based on the publicly available abstract.
Background.There is debate surrounding the effectiveness of the 23‐valent pneumococcal polysaccharide vaccine (PPV). We determined whether PPV was associated with reduced mortality or additional hospitalization for vaccine‐preventable infections in patients previously hospitalized for community‐acquired pneumonia (CAP).
Ok, so first thing to keep in mind: they only studied people who got pneumonia. This is not a study comparing vaccinated vs. unvaccinated, and seeing if there is any protection offered by the vaccine in the form of reduced infection rates. This is a study consisted of only people who got sick, breaking those down into two groups and seeing how each group fared.
Now, it is an accepted fact that no vaccine is 100% effective, meaning that no vaccine will prevent the disease on all people who receive it. For one reason or another, some people get no benefit from any given vaccine. Those people will get sick from the disease, regardless of their vaccination status. By definition, if you are gathering together people who are sick in the hospital, you are already limiting yourself to only that subset of the vaccinated population for whom the vaccine has already failed. So from that point alone, this is like saying “Well let me find all the people for whom the vaccine failed & let me measure how effective the vaccine was for them“. Just to make a comparison, this sounds kind of like saying “let me find out which team lost, and see how likely they are to have won!“.