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The Looming H5N1 Bird Flu Pandemic Vaccine Shortage

Recombinomics Commentary

August 7, 2005

Four different dosages were administered to the volunteers: 7.5 micrograms, 15 micrograms, 45 micrograms or 90 micrograms.

Fauci has said that tests have shown that the new vaccine produced a strong immune response among the volunteers, although the doses needed were higher than in the standard influenza vaccine offered each year.

Fauci said that, within a month, the vaccine will be tested on people ages 65 and over. After that, he said, it will be tested on children. He expressed confidence that they would confirm the success of the first tests and answer remaining scientific questions.

An earlier human vaccine against A(H5N1) avian influenza virus was prepared after it first appeared in the world, in Hong Kong in 1997. That vaccine was never fully developed or used, and the strain has mutated since then.

Because the vaccine is made in chicken eggs, "a potential major stumbling block" to successful mass production is the number of eggs farmers can supply manufacturers, Fauci said.

The above comments hint at the supply problem with the tested flu pandmeic vaccine.  The supply issue is in addition to the specificity issue.  Since the pandemic vaccine was made against the H and N gene products of a 2004 isolate from Vietnam, H5N1 has already started to evolve away from the vaccine being tested.  In the initial 2005 isolates from Vietnam there are 4 amino acid differences, but in the migratory bird sequences from Qinghai lake there are 18 differences, which would limit use of the pandemic vaccine on these isolates.  This H5N1 spreading across southern Russia and northern Kazakhstan is likely to spread throughout Europe and Asia, and possibly beyond.  If this strain achieves efficient human-to-human transmission, there will be significant specificity issues the vaccine under development.

Even if the emerging pandemic strain is closely related to the strains in Vietnam, there are still major production issues because the existing virus is not very immunogenic.  The dose response curve showed that increasing the amount of virus produced a stronger response, but the amount of virus required will cause significant production problems using FDA approved technology involving chicken eggs.

The initial testing was done on younger adults who are most likely to respond the best.  However, since two shots were used, it seems likely that using 90 micrograms in one shot did not produce a robust response.  Thus, it seems likely that two shots of 90 micrograms each will be required.  However, more might be required if the response from children or the 65 and older group produces a weaker response.  Because these tests have not been run, the proper dosage is not known.

However, even if the senior citizens and children match the younger adults, it seems that immunization would require at least 180 micrograms.  The current human trivalent vaccine uses 15 micrograms for each of three different viruses.  Thus, H5N1 immunization requires 12 times as much virus compared to a human virus.

Growing up that amount of virus will be a challenge, which might be exacerbated by rumors that the virus did not grow well in eggs.  Thus, combining a low yield of virus with a high requirement for dosage demonstrates why a looming pandemic vaccine shortage is a significant problem.

Clearly efforts need to be picked up a notch.  There could be several H5N1s that achieve efficient human-to-human transmission, as the virus dramatically expands it geographical and species host range via spread throughout Asia and Europe. 

H5N1 is serious.  Government responses are not.

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