Quote:
Originally Posted by serenitii  And they still aren't properly looking at the effects of the vaccine preventing carriage. The change in human reservoirs has been said to be one of the most important reasons why Hib cases are increasing in European countries.
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What's really irritating to me is that they're not setting up the present clinical trials in the countries where the vaccine is soon to be introduced, to observe the replacement disease.
Different public health agencies are taking different attitudes towards the global increase in NTHi where the Hib vaccine is used.
The CDC:
(March, 2007)
http://www.journals.uchicago.edu/doi...10.1086/511886
Quote:
| Of interest, Dworkin et al. [2] describe a significant increase in the reporting of invasive H. influenzae disease in people aged 65 years from 1.1 to 3.9 cases per 100,000 persons, which corresponds to an increase from 16 to 58 cases statewide per year |
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| Concern about the potential for vaccination to lead to an increase in invasive disease caused by nonvaccine types, or “replacement disease,” is not new. |
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| For the pneumococcal conjugate vaccine, emergence of nonvaccine types has started to occur—both among the target age group of young children [19, 20] and among HIV-infected adults [20]—but for both pneumococcal and H. influenzae type b conjugate vaccines, the substantial net benefit in disease reduction is still evident relative to the small increase of replacement types. |
So, they're calling NTHi a "replacement type".
Now, OTOH, the UK's HPA is saying "absolutely not!" to the idea of h-flu replacement.
In September of 2007, Raymond Tsang, (with the Vaccine Preventable Bacterial Diseases, National Microbiology Laboratory, Public Health Agency of Canada) wrote a little editorial in the Lancet that mentioned:
http://www.ncbi.nlm.nih.gov/pubmed/17714669
(sorry..you have to get the fulltext to read it)
Quote:
There is ample evidence of invasive
pneumococcal disease and invasive H influenzae
disease caused by capsule replacement strains after
introduction of the respective polysaccharide conjugate
vaccines |
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Now, for those of you who are familiar with the research on h-flu replacement, Tsang is the guy who published this:
http://www.journals.uchicago.edu/doi/abs/10.1086/518283
Quote:
| In addition to the proportional increase in cases of nontype b Haemophilus influenzae disease in the post H. influenzae type b vaccine era, the incidence of invasive H. influenzae disease was found to be approaching the rates of H. influenzae type b disease that were documented in the prevaccine period. Fifty-six percent of invasive disease now occurs in individuals aged >10 years. |
Anyway, back to the Lancet editorial, the HPA in the UK quickly responded to Tsang, saying:
http://www.ncbi.nlm.nih.gov/pubmed/18471770
(sorry again, you have to have the fulltext to read it)
Quote:
We read the comments of Raymond Tsang1 regarding
capsule replacement in vaccine-preventable diseases
and challenge the statement that “there is ample
evidence of…invasive Haemophilus infl uenzae disease
caused by capsule replacement strains after introduction
of…polysaccharide conjugate vaccines”. |
Then they talk about all the raw European data they have, and they run this analysis of a few countries and conclude:
Quote:
However, unlike the pneumococcal conjugate
vaccination programme, there is no consistent or robust
evidence to suggest that mass Hib vaccination in infancy
has led to serotype replacement in either carriage or
disease. |
As an aside, here's the raw data they ran their analysis from:
http://www.euibis.org/documents/2006_hib.pdf
...and they only used a few (cherry picked, I'd say) countries in their analysis, one of which is Iceland, which doesn't even report
anything besides B (mostly, according to table 2, page 14). I would love to have a discussion of that raw data, btw.
So then Tsang responds back to the HPA naysayers:
http://www.ncbi.nlm.nih.gov/pubmed/19022187
(sorry again, no free fulltext)
Quote:
The aim of my letter, “capsule switching and capsule
replacement in vaccine-preventable bacterial diseases”, was not to discredit the importance of vaccination against invasive bacterial disease, but to
highlight the importance of bacterial adaptability and the need for continued surveillance to stay ahead of the issues related to control of vaccine-preventable bacterial diseases. |
Quote:
Although invasive diseases caused by nonencapsulated H influenzae have not reached the level of disease burden posed by Hib in the pre-Hib vaccine era, their numbers are still disturbing and seem to
have increased in the past years, especially in adults, neonates, and elderly people.. |
Quote:
| Newer vaccines for control of all H influenzae strains, including the non-encapsulated strains, are currently in clinical trials. To define the patient population that would benefit most from such vaccine developments, we need to continue to strive for better surveillance data... |
There's overwhelming evidence that NTHi replaces Hib, and there's actually
no evidence that it doesn't.
But to settle the question once and for all, we'd need to evaluate all bacterial carriage and disease in a Hib clinical trial, in a Hib endemic area. We'd be arguing over the "realness" of Prevnar replacement if that had not been done in some PCV clinical trials.
