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!“.
Results.A total of 2950 patients were followed up for a median of 3.8 years. The mean patient age was 68 years; 52% were male. One‐third (n=956) received PPV: 667 (70%) before and 289 (30%) during hospitalization. After discharge, 1404 patients (48%) died, 504 (17%) were admitted with vaccine‐preventable infections, and 1626 (55%) reached the composite outcome of death or infection. PPV was not associated with reduced risk of the composite outcome (589 [62%] vs 1037 [52%] for those unvaccinated; adjusted hazard ratio [HR], 0.91; 95% confidence interval [CI], 0.79–1.04). Results were not altered in sensitivity analyses using propensity scores (adjusted HR, 0.91; 95% CI, 0.79–1.04), restricting the sample to patients 65 years or older (adjusted HR, 0.90; 95% CI, 0.77–1.04), or considering only those who received PPV at discharge (adjusted HR, 0.84; 95% CI, 0.71–1.00).
Second point to keep in mind; the mean patient age was 68 years. The study is itself limited to only “adults at high risk for pneumonia”. So at best, the results of this study might hold for adults, average 68 years old, for whom the vaccine has already failed to offer immune protection. That is quite a small subset of all people who get the vaccine. The question to ask ourselves is: how reliable are such results and how can they be applied to the total vaccinated population?
Conclusions.One‐half of patients discharged from the hospital after pneumonia die or are subsequently hospitalized with a vaccine‐preventable infection within 5 years. PPV was not associated with a reduced risk of death or hospitalization. Better pneumococcal vaccination strategies are urgently needed.
And this is the careless conclusions that I was referring to: “Better pneumococcal vaccination strategies are urgently needed.” Better than what? That is the confusing part. If you choose to only look at the people for whom the vaccine has already failed, what really do you expect the results to be? If the person got sick, the vaccine failed to protect them. If the vaccine failed, wouldn’t we expect both failed-vaccinated and unvaccinated groups to show the same pattern? What insight can one gain by looking at the failed vaccine group? Confirmation that a vaccine that failed to prevent the disease in the person, also fails to reduce mortality rates from the disease? So this study possibly tells us that in people over 68, when the pneumococcal vaccine fails, it fails completely. Hmm, ok, isn’t that kind of to be expected anyway?
How can these results support the conclusion that better pneumococcal vaccination strategies are urgently needed though? The study did not examine pneumococcal vaccine efficacy, like this one properly did, by comparing vaccinated vs. placebo shots and checking out infection and morbidity rates. The only question this study aimed to answer is this: When the vaccine fails to build immunity, does it also fail to protect from death? And the answer, unsurprisingly, is coming back to be yes.
Maybe some vaccines reduce death rates from the disease even if they fail to build immunity against the disease. I guess that is plausible; I don’t know enough to say. However, it appears to me that, the way this study was designed, the way the groups were chosen, leaves a lot to be desired and seems to be set up so as to provide only one possible answer. This study seems better equipped to figure out the mortality rate from pneumococcal than the efficacy of the pneumococcal vaccine. The authors should be more careful with their conclusions and keep in mind the limits of their design; they should be the first ones to acknowledge that their study cannot be generalized to the whole vaccinated population. Yet, somehow they fail to do that and instead make unwarranted conclusions about improving vaccination strategies. That coupled with journalists looking for sensational headlines unfortunately has the effect of sending a message to the public that is not supported by the science. And that is sad; sad and dangerous.
REMINDER: These comments should be held as temporary until I get my hands on the full PDF. That will either verify that my interpretation of the abstract is correct, or I will have to come back and modify my interpretation.