Sisyphus and the Conjugate Vaccines
As a punishment from the gods, Sisyphus was compelled to roll a huge rock up a steep hill, but before he reached the top of the hill, the rock always escaped him and he had to begin again. The maddening nature of the punishment was reserved for Sisyphus due to the mortal’s hubristic belief that his cleverness surpassed that of Zeus.
In September, the AP reported that Prevnar…
“A vaccine that has dramatically curbed pneumonia and other serious illnesses in children is having an unfortunate effect: promoting new superbugs that cause ear infections.”
I always wonder who actually writes these science stories you see in the media.
Yes, the emerging serotypes cause ear infections and other mild illnesses, but they also cause various deadly forms of invasive disease. It’s a phenomenon called “serotype replacement” (or “replacement disease” in other circumstances) and so far all of the conjugate vaccines (Hib, Prevnar, Menactra) have done this in some form or fashion. The vaccines work extremely well against vaccine-included serotypes of streptococcus pneumoniae, but they work so well that they also prevent asymptomatic carriage of these normally commensal organisms.
And that is a problem.
For example, from The Lancet:
“FINDINGS: We noted no reduction of AOM episodes in the pneumococcal vaccine group compared with controls (intention-to-treat analysis: rate ratio 1.25, 95% CI 0.99-1.57). Although nasopharyngeal carriage of pneumococci of serotypes included in the conjugate-vaccine was greatly reduced after pneumococcal vaccinations, immediate and complete replacement by non-vaccine pneumococcal serotypes took place.”
The human bacterial flora behaves as an ecosystem, and like any ecosystem, you can’t go around removing whole species of the local “wildlife” without unforeseen consequences. As much as I’d like to live in a world without mosquitoes, I wouldn’t go so far as to actually advocate taking on the eradication of all mosquitoes from Planet Earth. But that’s exactly the kind of thing the people in charge of international public health want to do.
Those in charge of the pneumococcal conjugate vaccine immunization program did forsee new pneumococcal serotypes moving in and filling the ecological niche left behind in the wake of Prevnar’s widespread use. But their plan to deal with this appears to be to continue adding more and more serotypes into the vaccine indefinately.
Presently, the clinical trials for a New and Improved Prevnar (PCV13, which will cover not only the old seven pneumococcal serotypes, but rather 13 serotypes) are nearing completion, and within a few years the Advisory Committee on Immunization Practices (also known as the ACIP) will be recommending it’s universal use.
Now, there are “only” 91 or so pneumococcal serotypes in total.
I suppose if worst came to worst, we could just have faith that the scientists at Wyeth Pharmaceuticals would keep on churning out more new and improved versions of Prevnar until we eventually reached PCV91 in, say, the year 2030.
Perhaps we could completely eradicate all streptococcus pneumoniae from the human bacterial flora, triumphing over nature!
Except…that won’t work, either.
It’s an ecosystem we’re dealing with here, remember?
Nevermind having to chase around the emerging pneumococcal serotypes for who knows how long. New pneumococcal serotypes replacing old pneumococcal serotypes is its own problem, but it’s more complicated than that. Entirely more complicated than that. So complicated that we only have “clues” about some of the aspects of this microscopic ecosystem.
From a scientific standpoint in the Journal of the American Medical Association:
Streptococcus pneumoniae carriage, specifically of vaccine-type strains, is negatively associated with S aureus carriage in children. The implications of these findings in the pneumococcal vaccine era require further investigation.”
As in, staphylococcus aureus?
Give people Prevnar and it makes them have more STAPH???
What does this increase in staph mean for us?