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Author Topic: Interpreting meaning in influenza vaccination study results  (Read 2741 times)

Offline DBecker1988

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Here is the study: newbielink:http://ije.oxfordjournals.org/content/35/2/337.full.pdf [nonactive]

The authors hypothesis is that those who get the influenza vaccination are more likely to be heath conscious individuals which might account for lower incidence of infection. I.E. healthy elders are motivated to be healthy and make healthy choices such as eating right, exercising, and getting their yearly vaccination. From this notion the author hypothesis that the main reason they are less likely to get sick is not from the vaccination, but rather from the other measures these people are taking to be healthy (exercise and diet)

That's all fine and dandy in theory, but I am having some issues interpreting how the results of the authors statistical analysis correlates with the conclusions. Perhaps someone who is more statistically inclined than myself can help by explaining the meaning of the results:


Results: The relative risk of death for vaccinated persons compared with unvaccinated persons was 0.39 [95% confidence interval (95% CI), 0.330.47] before influenza season, 0.56 (0.520.61) during influenza season, and 0.74 (0.670.80) after influenza season. The relative risk of pneumonia hospitalization was 0.72 (0.590.89) before, 0.82 (0.750.89) during, and 0.95 (0.851.07) after influenza season. Adjustment for diagnosis code variables resulted in estimates that were further from the null, in all time periods.

- What is the meaning of the numbers 0.39, 0.56, 0.72 etc.?

- How did these numbers come to be?

- Lastly, what does it mean that they consistently show the tendency to approach 1 with the progression of time? (see also table 5 on page 342)


One other confusing issue:

- Why is it that "healthy individuals" represent a demographic with more comorbidities? Isn't the reverse true? Perhaps I'm misinterpreting the data.


 

Offline cheryl j

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Does their risk analysis include the odds of an influenza virus mutating? The reason public health officials get so freaked out about influenza and sometimes are accused of crying wolf (eg swine flu in the 70s) is the distant memory of the 1918 flu that killed 50-100 million out of 1.8billion on the planet. Like SAARs it killed young healthy people because their immune systems reacted so violently to it. The muscle aches and pains were so bad, some people screamed when touched. Lungs filled with fluid and bubbles of gas, fevers were so high, that doctors sometimes thought they were dealing with malaria or dengue fever, or some other disease.  It killed 675,000 Americans out of 105 million. Britain lost 228,000. (I've posted the above information in an earlier discussion, I hope that is not considered cross posting as the topic was different)

I always though part of the reason for vaccinating is not just to provide immunity for the circulating virus but to provide partial immunity if it does mutate. Americans who came down with a milder form of flu in 1917 or 1916, did not get as sick when the mutated virus returned from Europe with soldiers after WWI.

Here is a vivid description of the 1918 flu:


"These men start with what appears to be an ordinary attack of la grippe or influenza," wrote Dr. Roy Grist, a Camp Devens physician, to a friend, "and when brought to the hospital they very rapidly develop the most vicious type of pneumonia that has ever been seen. Two hours after admission they have the mahogany spots over the cheekbones, and a few hours later you can begin to see cyanosis extending from their ears and spreading all over the face, until it is hard to distinguish the colored men from the white. . . . It is only a matter of a few hours then until death comes. . . . It is horrible. One can stand it to see one, two, or 20 men die, but to see these poor devils dropping like flies. . . . We have been averaging 100 deaths per day. . . . It takes special trains to carry away the dead. For several days there were no coffins and the bodies piled up something fierce."
 

Offline DBecker1988

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Thanks for the reply cheryl j,

The risk analysis does not include a mutation probability from what I can tell. I'm not sure how one would go about calculating this into the equation. Surly there is some sort of information regarding that matter somewhere. That 1918 flu sounds like serious stuff. I was totally unaware of this event up until now. Thanks for sharing.

Are you proficient in the method of statistical evaluation that this study utilizes?
 

Offline CliffordK

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I like the idea of comparing morbidity/mortality before, during, and after the flu season. 

I think they are calculating the Relative Risk for each group.  Then dividing the relative risk of the vaccinated by the unvaccinated. 

1 = no difference between the groups.
< 1 means higher morbidity/mortality in the unvaccinated group.
> 1 means higher morbidity/mortality in the vaccinated group.

0.5 would be about double (or half) the risk, which seems to be very significant.

The one thing that I find puzzling is Table 2 that seems to indicate that the vaccinated group was older, and had a higher rate of hypertension, lung disease, heart disease, diabetes, cancer, and etc. 

I find it difficult to conclude that those individuals are healthier in light of that table.

They may, of course, have more health care, or perhaps more likely to be up to date with other vaccinations such as pneumococcus.

It is also possible that the flu vaccines either give non-specific immunity, or it is possible that certain groups of elderly patients get exposed to the flu earlier than the commonly accepted "flu season".  I'm seeing in Table 1, that some individuals are getting vaccinated in September, with half of the vaccinations being given before mid October, before what they are considering the influenza season.

I think I would have also done a separation pre-vaccination/post-vaccination morbidity/mortality, rather than just pre-season.

"Experimenting" on humans is complex.  If the vaccine is considered "standard of care", it is difficult to justify withholding the care.  However, it would seem that one could do a similar study randomly assigning either nursing homes, or individuals in nursing homes to vaccine vs placebo groups.

Keep in mind the presumed benefits of "herd immunity" by vaccinating everyone within an environment such as a nursing home.
 

Offline cheryl j

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No, I don't know much about statistics.

The other odd thing about this issue, is that analyzing the risk of vaccinations isnt like the risk of, say, taking a medication that might have side effects. Vaccination protects not only  the individual but every unvaccinated people they come in contact with. With some infectious diseases the object isnt just to protect individuals but to eradicate the infectious agent once and for all. With influenza, that's probably impossible because of bird/pig animal hosts. 
 

Offline CliffordK

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The talked about the flu shot on the news yesterday.

Apparently in general, the flu shot gives about 56% lower chance getting the flu, but for the elderly that number drops down to about 27%.  This apparently has been known for some time, and they are currently trying experiments with higher dosages for the elderly group.

This year, however, the effectiveness was only about 9% for the elderly group.
 

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